hwc2: dump

Returns debug information that is displayed during `dumpsys SurfaceFlinger`.

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: Ib360640ee7b1d95a4be8b7043af98fa3761c89d4
7 files changed