hwc: hdmi: Use pluggable flag to determine HDMI library usage

The HDMI library is initialized for two HDMI use cases:
external and primary. In either case, we now rely on the
"pluggable" field of the panel information populated for each
interface. For example, if HDMI is primary, the "pluggable"
field in fb0's panel info node will be set to 1.

This change is intended to extend the usage of the HDMI library
to platforms that might use the DSI interface but with an HDMI
bridge chip, effectively creating a pluggable DSI interface.

Change-Id: I9a47e2b095d1a277c3626de29aa53437b137c1ac
11 files changed