drm/atomic: Add new reverse iterator over all plane state (V2)

drm/atomic: Add new reverse iterator over all plane state (V2)

Add reverse iterator for_each_oldnew_plane_in_state_reverse to
compliment the for_each_oldnew_plane_in_state way or reading plane
states.

The plane states are required to be read in reverse order for
amd drivers, cause the z order convention followed in linux is
opposite to how the planes are supposed to be presented to DC
engine, which is in common to both windows and linux.

V2: fix compile time errors due to -Werror flag.

Signed-off-by: Shirish S <shirish.s@amd.com>
Signed-off-by: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1520392203-6885-1-git-send-email-shirish.s@amd.com