drm/dsc: Define Display Stream Compression PPS infoframe

This patch defines a new header file for all the DSC 1.2 structures
and creates a structure for PPS infoframe which will be used to send
picture parameter set secondary data packet for display stream compression.
All the PPS infoframe syntax elements are taken from DSC 1.2 specification
from VESA.

v4:
* Remove redundant blankline in doc (Ville)
* use drm_dsc namespace for all structs (Ville)
* Use packed struct (Ville)
v3:
* Add the SPDX shorthand (Chris Wilson)
v2:
* Do not use bitfields in the struct (Jani Nikula)

Cc: Gaurav K Singh <gaurav.k.singh@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Acked-by: Sean Paul <seanpaul@chromium.org> (For merging through
drm-intel)
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181127214125.17658-2-manasi.d.navare@intel.com