compat_ioctl: block: handle Persistent Reservations

These were added to blkdev_ioctl() in linux-5.5 but not
blkdev_compat_ioctl, so add them now.

Cc: <stable@vger.kernel.org> # v4.4+
Fixes: bbd3e064 ("block: add an API for Persistent Reservations")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Fold in followup patch from Arnd with missing pr.h header include.

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