fs: Create a header file for filesystem-related commands

Most commands access the filesystem through the command-line interface
rather than the filesystem API itself. Add a new header file which
contains these functions, so we can separate commands from the API.

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/fat.c

@@ -10,7 +10,7 @@
 #include <command.h>
 #include <mapmem.h>
 #include <fat.h>
-#include <fs_legacy.h>
+#include <fs_cmd.h>
 #include <part.h>
 #include <asm/cache.h>