cleanup blk_execute_rq* v2

[Christoph Hellwig <hch@xxxxxx>]

Hi Jens,

this series cleans up the blk_execute_rq* helpers.  It simplifies the
plugging mess a bit, fixes the sparse __bitwise warnings and simplifies
the blk_execute_rq_nowait API a bit.

Changes since v1:
 - rebased to the current Linus tree with the nvme driver changes
   merged
 - fixed a trailing whitespace and odd formatting
 - fixed a mising semicolon in ufs