Always compile RenderEngine's Graphite backend

This will slightly increase SurfaceFlinger's binary size, but simplifies
the process of enabling Graphite. See b/327278664#comment13 for context.

Bug: b/327278664
Bug: b/341728634
Test: GraphiteVk and GaneshGL boot tests in presubmit
Flag: EXEMPT enablement of this feature is still guarded by other flags
Change-Id: I263af189291de74bd2a9dbb537fde5386f0adb22