OMAP4: DSS2: HDMI: HDMI driver addition in the DSS

Adding the hdmi interface driver(hdmi.c) to the dss driver. It configures
the audio and video portion of HDMI based on functionality called by the
panel driver.

Signed-off-by: Mythri P K <mythripk@ti.com>
Signed-off-by: Yong Zhi <y-zhi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>