SF: Add back debug control of HWC use

My changes to refactor Layer::setPerFrameData ended up dropping the
ability to force client composition if either mDebugDisableHWC or
mDebugRegion were set.

This simply adds back a check on those flags to force client
composition.

Test: Set "Disable HW overlays" developer option
Bug: 38853920

Change-Id: Ia31cca8232a95b081b1565921b18acd69fb02757