block: introduce blk_rq_is_passthrough

block: introduce blk_rq_is_passthrough

commit 57292b58ddb58689e8c3b4c6eadbef10d9ca44dd upstream.

This can be used to check for fs vs non-fs requests and basically
removes all knowledge of BLOCK_PC specific from the block layer,
as well as preparing for removing the cmd_type field in struct request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
[only take the blkdev.h changes as we only want the function for backported
patches - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>