update FatFS to R0.16 via abbrev/fatfs dependency

- Add lib/fatfs to deps_mandatory in get_deps.py, pinned to R0.16
  (commit 30ca13c6) from github.com/abbrev/fatfs mirror
- Move TinyUSB custom ffconf.h to examples/host/msc_file_explorer/src/
  with project-specific settings: FF_CODE_PAGE=437, FF_USE_LFN=1,
  FF_FS_RPATH=2, FF_VOLUMES=4, FF_FS_NORTC=1
- get_deps.py removes stock ffconf.h after clone to avoid conflict
- Remove vendored fatfs source files from git tracking

FatFS R0.16 includes important fixes since R0.15:
- Fixed FAT32 FsInfo regression (forced full FAT scan on f_getfree)
- Fixed f_readdir infinite loop (from R0.15b)
- f_getcwd/.. now works on exFAT
- Added FF_FS_CRTIME support