drm/i915/dp: Add a support of YCBCR 4:2:0 to DP MSA

When YCBCR 4:2:0 outputs is used for DP, we should program YCBCR 4:2:0 to
MSA and VSC SDP.

As per DP 1.4a spec section 2.2.4.3 [MSA Field for Indication of Color
Encoding Format and Content Color Gamut] while sending YCBCR 420 signals
we should program MSA MISC1 fields which indicate VSC SDP for the Pixel
Encoding/Colorimetry Format.

v2: Block comment style fix.

v6:
  Fix an wrong setting of MSA MISC1 fields for Pixel Encoding/Colorimetry
  Format indication. As per DP 1.4a spec Table 2-96 [MSA MISC1 and MISC0
  Fields for Pixel Encoding/Colorimetry Format Indication]
  When MISC1, bit 6, is Set to 1, a Source device uses a VSC SDP to
  indicate the Pixel Encoding/Colorimetry Format. On the wrong version
  it set a bit 5 of MISC1, now it set a bit 6 of MISC1.

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190521121721.32010-5-gwan-gyeong.mun@intel.com