Implement cec message cache.

HDMI bus for CEC is quite slow and it may cause conflict
or timeout during device discovery stage or hot-plug
detection stage. However, some static information, such
as physical address, vendor id or osd name are usually
sent automatically when a device is connected, and
almost never change after updated.

Change-Id: I4df9d27ef1af04ee35d63a764580fed07c32d15d