drm_hwcomposer: Use a vector for composition source_layers

Instead of a 1:1 mapping of layer:plane, use a vector to store
source layers for a composition plane. This will allow us to
represent squash compositions more easily by adding all source
layers to the vector.

This should also facilitate hardware which allows multiple fbs per plane.

TEST=Tested on ryu

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Change-Id: I5d4bfc6e9da022eaab047f948cc874d6a8a25746
3 files changed