[DO NOT MERGE] make_f2fs: issue discard commands on mkfs

We'd better to discard whole partition for better performance.

Bug: 112868088
Test: factory reset
Change-Id: I9c0c711f2b081e4d0b4e145ab08f95b382925847
Merged-In: I9c0c711f2b081e4d0b4e145ab08f95b382925847
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
(cherry picked from commit e42a4945929a4bb1b2ef7e74093ce0882ff81b8d)