Extended lfsr_mount to accept mount flags

This has been a long-time coming, mount flags are just too useful for
configuring a filesystem at runtime.

Currently this is limited to LFS_M_RDONLY and LFS_M_CKPROGS, but there
are a few more planned in the future:

  LFS_M_RDWR     = 0x0000, // Mount the filesystem as read and write
  LFS_M_RDONLY   = 0x0001, // Mount the filesystem as readonly
  LFS_M_STRICT*  = 0x0002, // Error if on-disk config does not match
  LFS_M_FORCE*   = 0x0004, // Ignore compat flags, mount readonly
  LFS_M_FORCEWITHRECKLESSABANDON*
                 = 0x0008, // Ignore compat flags, mount read write

  LFS_M_CKPROGS  = 0x0010, // Check progs by reading back progged data
  LFS_M_CKREADS* = 0x0020, // Check reads via checksums

  * Hypothetical

As a convenience, we also return mount flags in the struct lfs_fsinfo's
flags field as their relevant LFS_I_* variants. Though only to match
statvfs, and only because it's cheap, littlefs's API is low-level and we
should expect users to know what flags they passed to lfsr_mount.

As for the new mount flags:

- LFS_M_RDONLY - For consistency with existing APIs, this just asserts
  on write operations, which makes it a bit useless... But the info flag
  LFS_I_RDONLY may be useful for falling back to a readonly mode if
  we encounter on-disk compat issues.

  At least if implement the theoretical LFS_UNTRUSTED_USER mode
  LFS_M_RDONLY could become a runtime error.

- LFS_M_RDWR - This really just exists to compliment LFS_M_RDONLY and to
  match LFS_O_RDONLY/LFS_O_RDWR. It's just an alias for 0, and I don't
  think there will ever be a reason to make it non-0 (but I can always
  be wrong!).

- LFS_M_CKPROGS - This replaces the check_progs config option and avoids
  using a full byte to store a bool.

  We should probably also have a compile-time option to compile this out
  (LFS_NO_CKPROGS?), but that's a future thing to do.

This ended up adding a surprising bit of code, considering we're just
moving flags around, and noise in lfs_alloc added a bit of stack again:

           code          stack
  before: 35880           2672
  after:  35932 (+0.1%)   2680 (+0.3%)

runners/bench_runner.h

@@ -126,7 +126,6 @@ void bench_permutation(size_t i, uint32_t *buffer, size_t size);
     BENCH_DEFINE(SHRUB_SIZE,         INLINE_SIZE                            ) \
     BENCH_DEFINE(FRAGMENT_SIZE,      BLOCK_SIZE/8                           ) \
     BENCH_DEFINE(CRYSTAL_THRESH,     BLOCK_SIZE/8                           ) \
-    BENCH_DEFINE(CHECK_PROGS,        false                                  ) \
     BENCH_DEFINE(ERASE_VALUE,        0xff                                   ) \
     BENCH_DEFINE(ERASE_CYCLES,       0                                      ) \
     BENCH_DEFINE(BADBLOCK_BEHAVIOR,  LFS_EMUBD_BADBLOCK_PROGERROR           ) \
@@ -156,8 +155,7 @@ void bench_permutation(size_t i, uint32_t *buffer, size_t size);
     .inline_size        = INLINE_SIZE,          \
     .shrub_size         = SHRUB_SIZE,           \
     .fragment_size      = FRAGMENT_SIZE,        \
-    .crystal_thresh     = CRYSTAL_THRESH,       \
-    .check_progs        = CHECK_PROGS,
+    .crystal_thresh     = CRYSTAL_THRESH,
 
 #define BENCH_BDCFG \
     .erase_value        = ERASE_VALUE,          \

runners/test_runner.h

@@ -111,7 +111,6 @@ void test_permutation(size_t i, uint32_t *buffer, size_t size);
     TEST_DEFINE(SHRUB_SIZE,         INLINE_SIZE                             ) \
     TEST_DEFINE(FRAGMENT_SIZE,      BLOCK_SIZE/8                            ) \
     TEST_DEFINE(CRYSTAL_THRESH,     BLOCK_SIZE/8                            ) \
-    TEST_DEFINE(CHECK_PROGS,        false                                   ) \
     TEST_DEFINE(ERASE_VALUE,        0xff                                    ) \
     TEST_DEFINE(ERASE_CYCLES,       0                                       ) \
     TEST_DEFINE(BADBLOCK_BEHAVIOR,  LFS_EMUBD_BADBLOCK_PROGERROR            ) \
@@ -141,8 +140,7 @@ void test_permutation(size_t i, uint32_t *buffer, size_t size);
     .inline_size        = INLINE_SIZE,          \
     .shrub_size         = SHRUB_SIZE,           \
     .fragment_size      = FRAGMENT_SIZE,        \
-    .crystal_thresh     = CRYSTAL_THRESH,       \
-    .check_progs        = CHECK_PROGS,
+    .crystal_thresh     = CRYSTAL_THRESH,
 
 #define TEST_BDCFG \
     .erase_value        = ERASE_VALUE,          \