minified version of FATFS

[Syphurith]

#define _FS_MINIMIZE    0   /* 0 to 3 */
/* The _FS_MINIMIZE option defines minimization level to remove API functions.
/
/   0: All basic functions are enabled.
/   1: f_stat(), f_getfree(), f_unlink(), f_mkdir(), f_chmod(), f_utime(),
/      f_truncate() and f_rename() function are removed.
/   2: f_opendir(), f_readdir() and f_closedir() are removed in addition to 1.
/   3: f_lseek() function is removed in addition to 2. */

As mentioned above in FATFS ffconf.h, this could remove several functions.
I've checked and find no usage of those except f_lseek, from compiled binary.
This would decrease the binary size by almost 2KB.
But be aware: please reject this if planned to use those functions later.