block: fixes to compile with LK 3.0

Change-Id: Iad0b391d8f0d02ed0efcda619e954ceb678f9710
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
block: add REQ_URGENT to request flags

This patch adds a new flag to be used in cmd_flags field of struct request
for marking request as urgent.
Urgent request is the one that should be given priority currently handled
(regular) request by the device driver. The decision of a request urgency
is taken by the scheduler.

Change-Id: Ic20470987ef23410f1d0324f96f00578f7df8717
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: zwliew <zhaoweiliew@gmail.com>

Conflicts:
	include/linux/blk_types.h