hwc2: get and accept display changes

If the client calls validate display and there are display changes/requests, the
client can query the changes/requests and choose to accept them.

Test: Add "TARGET_USES_HWC2 := true" to BoardConfig.mk.
      Recompile.
      Run testcases: https://android-review.googlesource.com/#/q/project:
            platform/frameworks/native+branch:master+topic:test-hwc2

Change-Id: I2b8a49119b5efa7394e67e810592e840f18b81ae
4 files changed