zbd: support 'z' suffix for zone granularity

zbd: support 'z' suffix for zone granularity

Allow users to pass some options with zone granularity which is natural
for ZBD workloads.

This is nifty for writing quick tests and when firmware guys change
zone sizes.

Converted options are

	io_size=
	offset=
	offset_increment=
	size=
	zoneskip=

Example:

	rw=write
	numjobs=2
	offset=1z
	offset_increment=10z
	size=5z
	io_size=6z

Thread 1 will write zones 1, 2, 3, 4, 5, 1.
Thread 2 will write zones 11, 12, 13, 14, 15, 11.

Note:
	zonemode=strided doesn't create ZBD zone structure but requires
	value recalculation. This is why 2 functions are split.

Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>