drm/i915/vdsc: Fill the intel_dsc_get_pps_config function

We have setup both the read and write functions so we can
move ahead and fill in all the readout state from PPS register
into the crtc_state so we can send it for comparision.

--v2
-Shorten comment to just PPSX rather than having the whole
"Readout PPSX register" [Jani]
-Remove pps_temp reinitialization as its being initialized in
the read function [Jani]
-Use REG_FIELD_GET to readout certain fields of dsc registers
[Jani]

--v9
-Place the masks at a more appropriate place [Ankit]

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230828054300.560559-8-suraj.kandpal@intel.com