drm_hwcomposer: Add type to DrmCompositionPlane

Instead of encoding the plane/composition type in source_layer,
move it to its own explicit type. This will allow us to expand
source_layer to include more than one layer.

BUG=b/28117135
TEST=compiles and runs on smaug

Change-Id: I19b1ed8e395347bbefb0fb6a0ab02d6ac0e5c1c1
Signed-off-by: Sean Paul <seanpaul@chromium.org>
3 files changed