block: move a few definitions out of CONFIG_BLK_DEV_ZONED

Allow using a few symbols with IS_ENABLED instead of #idef by moving
the declarations out of #idef CONFIG_BLK_DEV_ZONED, and move
bdev_nr_zones into the remaining  #idef CONFIG_BLK_DEV_ZONED, #else
block below.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231127072002.1332685-1-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>