drm_hwcomposer: only check the composition after a geometry change

Do not check the composition with kernel for every frame. We are currently
using synchronous atomic ioctl calls, so all test-only calls are serialized
with the actual commits.

BUG=25866352
TEST=same test procedure as crosbug.com/p/47206

Change-Id: Ia423243c279fc677ff6213115a8f20efa40c235e
2 files changed