drm/dsc: Split DSC PPS and SDP header initialisations

The DP 1.4 spec defines the SDP header and SDP contents for
a Picture Parameter Set (PPS) that must be sent in advance
of DSC transmission to define the encoding characteristics.

This was done in one struct, drm_dsc_pps_infoframe, which
conatined the SDP header and PPS.  Because the PPS is
a property of DSC over any connector, not just DP, and because
drm drivers may have their own SDP structs they wish to use,
make the functions that initialise SDP and PPS headers take
the components they operate on, not drm_dsc_pps_infoframe,

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190221202001.28430-4-David.Francis@amd.com