drm/kmb: Enable alpha blended second plane

Enable one additional plane that is alpha blended on top
of the primary plane.

This also fixes the below warnings when building with
-Warray-bounds:

drivers/gpu/drm/kmb/kmb_plane.c:135:20: warning: array subscript 3 is
above array bounds of 'struct layer_status[1]' [-Warray-bounds]
drivers/gpu/drm/kmb/kmb_plane.c:132:20: warning: array subscript 2 is
above array bounds of 'struct layer_status[1]' [-Warray-bounds]
drivers/gpu/drm/kmb/kmb_plane.c:129:20: warning: array subscript 1 is
above array bounds of 'struct layer_status[1]' [-Warray-bounds]

v2: corrected previous patch dependecies so it builds

Signed-off-by: Edmund Dea <edmund.j.dea@intel.com>
Signed-off-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20210728003126.1425028-13-anitha.chrisanthus@intel.com/


Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>