f2fs: Reset sequential zones on zoned block devices

When a zoned block device is mounted, discarding sections
contained in sequential zones must reset the zone write pointer.
For sections contained in conventional zones, the regular discard
is used if the drive supports it.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

 Conflicts:
	fs/f2fs/segment.c