drm: Rename struct edp_vsc_psr to struct dp_sdp

VSC SDP Payload for PSR is one of data block type of SDP (Secondaray Data
Packet). In order to generalize SDP packet structure name, it renames
struct edp_vsc_psr to struct dp_sdp. And each SDP data blocks have
different usages, each SDP type has different reserved data blocks and
Video_Stream_Configuration Extension VESA SDP might use all of Data Blocks
as Extended INFORFRAME Data Byte. so it makes Data Block variables as
array type. And it adds comments of details of DB of VSC SDP Payload
for Pixel Encoding/Colorimetry Format. This comments follows DP 1.4a spec,
section 2.2.5.7.5, chapter "VSC SDP Payload for Pixel Encoding/Colorimetry
Format".

v7: Addressed review comments from Ville.

v9: Rename a member value name DB to db on struct dp_sdp [Laurent]

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190521121721.32010-3-gwan-gyeong.mun@intel.com