Changed callbacks to take user-provided context directly

This is a style change to make littlefs's callbacks consistent with most
callback declarations found in C. That is, taking in a user-provided
`void*`.

Previously, these callbacks took a pointer to the config struct itself,
which indirectly contained a user provided context, and this gets the
job done, but taking in a callback with a `void*` is arguably more
expected, has a better chance of integrating with C++/OS-specific code,
and is more likely to be optimized out by a clever compiler.

---

As a part of these changes, the geometry for the test bds needed to be
moved into bd specific configuration objects. This is a good change as
it also allows for testing situations where littlefs's geometry does not
match the underlying bd.

lfs.h

@@ -130,28 +130,28 @@ enum lfs_whence_flags {
 struct lfs_cfg {
     // Opaque user provided context that can be used to pass
     // information to the block device operations
-    void *context;
+    void *ctx;
 
     // Read a region in a block. Negative error codes are propogated
     // to the user.
-    int (*read)(const struct lfs_cfg *c, lfs_block_t block,
+    int (*read)(void *ctx, lfs_block_t block,
             lfs_off_t off, void *buffer, lfs_size_t size);
 
     // Program a region in a block. The block must have previously
     // been erased. Negative error codes are propogated to the user.
     // May return LFS_ERR_CORRUPT if the block should be considered bad.
-    int (*prog)(const struct lfs_cfg *c, lfs_block_t block,
+    int (*prog)(void *ctx, lfs_block_t block,
             lfs_off_t off, const void *buffer, lfs_size_t size);
 
     // Erase a block. A block must be erased before being programmed.
     // The state of an erased block is undefined. Negative error codes
     // are propogated to the user.
     // May return LFS_ERR_CORRUPT if the block should be considered bad.
-    int (*erase)(const struct lfs_cfg *c, lfs_block_t block);
+    int (*erase)(void *ctx, lfs_block_t block);
 
     // Sync the state of the underlying block device. Negative error codes
     // are propogated to the user.
-    int (*sync)(const struct lfs_cfg *c);
+    int (*sync)(void *ctx);
 
     // Minimum size of a block read. All read operations will be a
     // multiple of this value.
@@ -266,15 +266,6 @@ int lfs_sync(void);
 #ifndef LFS_LOOKAHEAD_BUFFER
 #define LFS_LOOKAHEAD_BUFFER NULL
 #endif
-#ifndef LFS_NAME_MAX
-#define LFS_NAME_MAX 0
-#endif
-#ifndef LFS_FILE_MAX
-#define LFS_FILE_MAX 0
-#endif
-#ifndef LFS_ATTR_MAX
-#define LFS_ATTR_MAX 0
-#endif
 #endif
 
 #if !defined(LFS_FILE_STATICCFG)