Moved ckprogs behind LFS_CKPROGS ifdef

So just like ckreads, ckprogs is now opt-in, requiring both 1. defining
LFS_CKPROGS at compile-time, and 2. passing the LFS_M_CKPROGS flag
during lfsr_mount.

_Unlike_ ckreads, ckprogs is actually a very lightweight feature. So the
difference between compiling with/without ckprogs is really quite small:

                code          stack
  before:      36480           2680
  yes-ckprogs: 36480 (+0.0%)   2680 (+0.0%)
  no-ckprogs:  36428 (-0.1%)   2680 (+0.0%)

It's almost not worth putting behind an ifdef if not for consistency
with ckreads.

tests/test_ck.toml

@@ -477,6 +477,7 @@ defines.BADBIT = -1
 defines.BADBLOCK_BEHAVIOR = 'LFS_EMUBD_BADBLOCK_PROGFLIP'
 # this should stay inlined
 defines.SIZE = 'BLOCK_SIZE/16'
+ifdef = 'LFS_CKPROGS'
 code = '''
     // test all bad bits in the mroot
     for (lfs_size_t i = 0;
@@ -555,6 +556,7 @@ defines.BADBIT = -1
 defines.BADBLOCK_BEHAVIOR = 'LFS_EMUBD_BADBLOCK_PROGFLIP'
 # this should create a single block file
 defines.SIZE = 'BLOCK_SIZE'
+ifdef = 'LFS_CKPROGS'
 code = '''
     // first we need to figure out where the data block will actually
     // end up, fortunately our block randomization is intentionally
@@ -664,6 +666,7 @@ defines.INLINE_SIZE = 0
 defines.CRYSTAL_THRESH = -1
 defines.FRAGMENT_SIZE = 'BLOCK_SIZE/8'
 defines.SIZE = '2*FRAGMENT_SIZE'
+ifdef = 'LFS_CKPROGS'
 code = '''
     // first we need to figure out where the btree block will actually
     // end up, fortunately our block randomization is intentionally