Define bdev_is_zoned(), bdev_zone_sectors() and bdev_get_queue() earlier
in the blkdev.h include file. Simplify bdev_is_zoned() by removing the
superfluous NULL check for request queue while we are at it.
This commit has no functional change, and it is a prep patch for allowing
zoned devices with non-power-of-2 zone sizes in the block layer.