drm/i915/dsc: fix DSS CTL register usage for ICL DSI transcoders

Use the correct DSS CTL registers for ICL DSI transcoders.

As a side effect, this also brings back the sanity check for trying to
use pipe DSC registers on pipe A on ICL.

Fixes: 8a029c11 ("drm/i915/dp: Modify VDSC helpers to configure DSC for Bigjoiner slave")
References: http://lore.kernel.org/r/87eegxq2lq.fsf@intel.com
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: <stable@vger.kernel.org> # v5.11+
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210319115333.8330-1-jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_vdsc.c

@@ -1014,20 +1014,14 @@ static i915_reg_t dss_ctl1_reg(const struct intel_crtc_state *crtc_state)
 {
 	enum pipe pipe = to_intel_crtc(crtc_state->uapi.crtc)->pipe;
 
-	if (crtc_state->cpu_transcoder == TRANSCODER_EDP)
-		return DSS_CTL1;
-
-	return ICL_PIPE_DSS_CTL1(pipe);
+	return is_pipe_dsc(crtc_state) ? ICL_PIPE_DSS_CTL1(pipe) : DSS_CTL1;
 }
 
 static i915_reg_t dss_ctl2_reg(const struct intel_crtc_state *crtc_state)
 {
 	enum pipe pipe = to_intel_crtc(crtc_state->uapi.crtc)->pipe;
 
-	if (crtc_state->cpu_transcoder == TRANSCODER_EDP)
-		return DSS_CTL2;
-
-	return ICL_PIPE_DSS_CTL2(pipe);
+	return is_pipe_dsc(crtc_state) ? ICL_PIPE_DSS_CTL2(pipe) : DSS_CTL2;
 }
 
 void intel_dsc_enable(struct intel_encoder *encoder,