Add HDMI support to Beaglebone Black:

• Add driver for TDA19988 HDMI framer
• Add simple interface to communicate with HDMI sink: read EDID and set videomode
• Add event-based API to notify LCD controller when HDMI sink is available
• Add HDMI framer node and add refernce to it to lcdc node. This part of DTS tree is custom and does not match Linux DTS because Linux uses combination of pseudo-node in DTS and hardcoded driver information that does not map to our model.