fs: littlefs: remove dependency on flash map from FILE_SYSTEM_LITTLEFS

LittleFS may be used not only for Flash devices, we can use it for block
devices too. So, I have changed dependency rules and remove dependency
on flash map from FILE_SYSTEM_LITTLEFS.

Signed-off-by: Laczen JMS <laczenjms@gmail.com>
Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>