drm/i915/dp: Read out DP SDPs

It adds code to read the DP SDPs from the video DIP and unpack them into
the crtc state.

It adds routines that read out DP VSC SDP and DP HDR Metadata Infoframe SDP
In order to unpack DP VSC SDP, it adds intel_dp_vsc_sdp_unpack() function.
It follows DP 1.4a spec. [Table 2-116: VSC SDP Header Bytes] and
[Table 2-117: VSC SDP Payload for DB16 through DB18]

In order to unpack DP HDR Metadata Infoframe SDP, it adds
intel_dp_hdr_metadata_infoframe_sdp_unpack(). And it follows DP 1.4a spec.
([Table 2-125: INFOFRAME SDP v1.2 Header Bytes] and
[Table 2-126: INFOFRAME SDP v1.2 Payload Data Bytes - DB0 through DB31])
and CTA-861-G spec. [Table-42 Dynamic Range and Mastering InfoFrame].

A naming rule and style of intel_read_dp_sdp() function references
intel_read_infoframe() function of intel_hdmi.c

v2: Minor style fix
v3: Replace a structure name to drm_dp_vsc_sdp from intel_dp_vsc_sdp
v4: Use struct drm_device logging macros
v5: Addressed review comments from Uma
  - Polish commit message and comments
  - Combine the if checks of sdp.HB2 and sdp.HB3
  - Add 6bpc to unpacking of VSC SDP

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200514060732.3378396-3-gwan-gyeong.mun@intel.com