drm/amd/display: Add DPCS regs for dcn3 link encoder

dpcs reg are missing for dcn3 link encoder regs list, so add them.

Also remove
DPCSTX_DEBUG_CONFIG and RDPCSTX_DEBUG_CONFIG as they are unused and
cause compile errors for dcn3

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>