drm/dp: Define payload size for DP SDP PPS packet

DP 1.4 spec defines DP secondary data packet for DSC
picture parameter set. This patch defines its payload size
according to the DP 1.4 specification.

Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Gaurav K Singh <gaurav.k.singh@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@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/20181031001923.31442-7-manasi.d.navare@intel.com