Revert "block: fix genhd refcounting in blkio_policy_parse_and_set()"

This reverts commit 8104280b742aaa9fe736bb3c0415a8a09d864983.
Revert "block/blk-sysfs.c: fix kerneldoc references"

This reverts commit fa3f79647c19688c41851b8a60bc9cef6dd18654.
Revert "block: document blk-plug"

This reverts commit 1ce1278b6bbfef06a9ae6e3d3a7f845c759097df.
Revert "block: refactor generic_make_request"

This reverts commit 351fac61b0cad435c6bb2b22d6ce088bd888bf18.
Revert "block: remove support for bio remapping from ->make_request"

This reverts commit bcf320cac2fabfe995707c6e02197d899d9aa439.