drm/dsc: use rc_model_size from DSC config for PPS

The PPS is supposed to reflect the DSC config instead of hard coding the
rc_model_size. Make it so.

Currently all users of drm_dsc_pps_payload_pack() hard code the size to
8192 also in the DSC config, so this change should have no impact, other
than allowing the drivers to use other sizes as needed.

Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c3246aff585efcd728ee3dc96f52db5e46f6a162.1607429866.git.jani.nikula@intel.com