FROMLIST: null_blk: allow zoned devices with non power-of-2 zone sizes

Convert the power-of-2(po2) based calculation with zone size to be generic
in null_zone_no with optimization for po2 zone sizes.

The nr_zones calculation in null_init_zoned_dev has been replaced with a
division without special handling for po2 zone sizes as this function is
called only during the initialization and will not be invoked in the hot
path.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed by: Adam Manzanares <a.manzanares@samsung.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Bug: 197782466
Bug: 269471019
Link: https://lore.kernel.org/linux-block/20220923173618.6899-7-p.raghav@samsung.com/


Change-Id: I8d1a915e6e09b04095acdf964d31837c4206bc49
Signed-off-by: Bart Van Assche <bvanassche@google.com>