remove the cmd_type field from struct request

[Christoph Hellwig]

Hi Jens,

this series gets rid of the cmd_type field in struct request and
instead folds it into the REQ_OP* space.  This reduces the size of
struct request, and leads to a single op namespace that drivers
can easily switch on.  Except for the legacy ide driver which has
a mess of different request types [1] this also nicely cleans up the
code.

Note that the patches are on top of the

    "make SCSI passthrough support optional"

series I sent out on Saturday.  To make life easier I also have a git
tree available here:

	git://git.infradead.org/users/hch/block.git cmd_type

	http://git.infradead.org/users/hch/block.git/shortlog/refs/heads/cmd_type

[1] which were a pain in the ass to untangle and debug during development,
it's really time for it to die..