fs_mgr: add support for "sync" mount flag

Change-Id: I6ad74cfbf98d30320785e3691df30dabc5c54cb9
(cherry picked from commit ba8e7e9acb369632286f5dc210a6dff83250cf86)
Revert "Fix gr_text() syntax until minui gets updated"

This reverts commit 78dfb9a053e0afa1d70f4e57205feeb072ccc0b8.

(cherry picked from commit 77fbd1dbf188df9a9812e7053fec6457673e119c)