Use "HWUI" LOG_TAG exclusively in libs/hwui/**

"OpenGLRenderer" is no longer accurate, and jreck@ has expressed a
desire to have all logging unified under one tag to allow for filtering,
as logcat is quite noisy.

Bug: N/A
Test: builds and *seems* to pass a quick "#ifndef LOG_TAG" check to
see if LOG_TAG is ever overridden outside of this Android.bp

Change-Id: I8b5413f20a85fb9615bd38778c3262790b7225bf