base

CEC: Define a system property to keep playback device awake

Playback device doesn't go to suspend (standby) mode if it's
the active source. This CL makes the behavior configurable through
the system property persist.sys.hdmi.keep_awake.

Bug: 19299723
Change-Id: Icb8b593ab44429ec0520e60d19d0368982ff5667