OMAP4: HDMI: Add HDMI structure in the board file for OMAP4 SDP

Adding  board file structure for display which adds the display
structure with HDMI as the default driver when the display init
is called.
HDMI GPIO configurations are also done in this file.

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