drm_hwcomposer: Move SeparateLayers into a member function

Instead of passing a bunch of member data to a static function, make
SeparateLayers a member of DrmDisplayComposition. This will be simplified
further once the Planner interface is implemented.

BUG=b/28117135
TEST=Tested on ryu

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Change-Id: Ia4e15aa20b6dc14b044ee1dec7b5fce514278be7
2 files changed