Adjust the LUT test

* Only send an sRGB layer if the device *really* doesn't support HLG, to
  accomodate more devices.
* Enforce that we hit device composition
* Destroy the layer under test at the end, as we test with multiple
  colormodes

Bug: 418740883
Flag: TEST_ONLY
Test: VtsHalGraphicsComposer3_ReadbackTest

Change-Id: I5ac4ae87ff095c796387b6ba14c9bda6f044ba2a
1 file changed