mkfs: support passing in the number of sectors to use

Adds the optional sectors count:
  mkfs.f2fs [options] device [sectors]

Change-Id: I3ac83121576574bda074140ffa60195a2bc9947b

Signed-off-by: JP Abgrall <jpa@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2 files changed