OMAP: DSS2: Add new color formats for OMAP4

Add new color formats supported by OMAP4: NV12, RGBA16, RGBX16,
ARGB16_1555, XRGB16_1555.
NV12 color format is defined here, its support in DSS will be added separately.

Signed-off-by: Amber Jain <amber@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>