surfaceflinger: add support for android.hardware.graphics

This adds a new path to HWC2 to use
android.hardware.graphics.composer@2.1::IComposer instead of hwcomposer2.
Which path to use is determined by whether BYPASS_IHWC is set at compile
time.  When it is set, the old path, kept for HWC2On1Adapter, is used.
When it is not set, the new path is taken.

BYPASS_IHWC2 is set when TARGET_USES_HWC2 is not.

Test: Maps, Camera, YouTube, etc.
Change-Id: I37aceafd1733fa9f76e7f7db4f59ad4776415306