OMAP: DSS2: Add support for NV12 format

Add the support for NV12 color format.
Configure base address for UV component of NV12 color format.
Change the way chroma scaling is handled for YUV formats on OMAP4 by enabling
chroma-resampling for video pipeline and hence using FIR2 register set for
scaling UV.
Changes to _dispc_set_scaling(), because of the reason above, are:
- call _dispc_set_scaling_common() to handle scaling for all color formats
  except for OMAP4 where it only handles scaling for RGB or Y-component
- call _dispc_set_scaling_uv() for special handling required for UV
  component on OMAP4.
- dispc_set_scaling_uv() also resets chroma-resampling bit for RGB color modes.

Contains chroma scaling (_dispc_set_scaling_uv) design and implemented by
Lajos Molnar <molnar@ti.com>

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