drm/i915/rkl: Don't try to access transcoder D

There are a couple places in our driver that loop over transcoders A..D
for gen11+; since RKL only has three pipes/transcoders, this can lead to
unclaimed register reads/writes. We should add checks for transcoder
existence where appropriate.

v2: Move one transcoder check that wound up in the wrong function after
conflict resolution. It belongs in bdw_get_trans_port_sync_config
rather than bxt_get_dsi_transcoder_state.

v3: Switch loops to use for_each_cpu_transcoder_masked() since this
iterator already checks the platform's transcoder mask for us.
(Ville)

Cc: Aditya Swarup <[e-mail]>
Cc: Ville Syrjälä <[e-mail]>
Signed-off-by: Matt Roper <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Reviewed-by: Ville Syrjälä <[e-mail]>

drivers/gpu/drm/i915/i915_irq.c

···
 {
 	struct intel_uncore *uncore = &dev_priv->uncore;
 	enum pipe pipe;
+	u32 trans_mask = BIT(TRANSCODER_A) | BIT(TRANSCODER_B) |
+		BIT(TRANSCODER_C) | BIT(TRANSCODER_D);
 
 	intel_uncore_write(uncore, GEN11_DISPLAY_INT_CTL, 0);
 
 	if (INTEL_GEN(dev_priv) >= 12) {
 		enum transcoder trans;
 
-		for (trans = TRANSCODER_A; trans <= TRANSCODER_D; trans++) {
+		for_each_cpu_transcoder_masked(dev_priv, trans, trans_mask) {
 			enum intel_display_power_domain domain;
 
 			domain = POWER_DOMAIN_TRANSCODER(trans);
···
 	u32 de_port_masked = gen8_de_port_aux_mask(dev_priv);
 	u32 de_port_enables;
 	u32 de_misc_masked = GEN8_DE_EDP_PSR;
+	u32 trans_mask = BIT(TRANSCODER_A) | BIT(TRANSCODER_B) |
+		BIT(TRANSCODER_C) | BIT(TRANSCODER_D);
 	enum pipe pipe;
 
 	if (INTEL_GEN(dev_priv) <= 10)
···
 	if (INTEL_GEN(dev_priv) >= 12) {
 		enum transcoder trans;
 
-		for (trans = TRANSCODER_A; trans <= TRANSCODER_D; trans++) {
+		for_each_cpu_transcoder_masked(dev_priv, trans, trans_mask) {
 			enum intel_display_power_domain domain;
 
 			domain = POWER_DOMAIN_TRANSCODER(trans);