drm/blend: Use new atomic iterator macros.

There are new iterator macros that annotate whether the new or old
state should be used. This is better than using a state that depends on
whether it's called before or after swap. For clarity, also rename the
variables from $obj_state to (old,new)_$obj_state as well.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487256430-7625-6-git-send-email-maarten.lankhorst@linux.intel.com


Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>