drm/i915/bxt: add dsi transcoders

The BXT display connections have DSI transcoders A and C that can be
muxed to any pipe, not unlike the eDP transcoder. Add the notion of DSI
transcoders.

The "normal" transcoders A, B and C are not used with BXT DSI, so care
must be taken to avoid accessing those registers with DSI transcoders in
the hardware state readout, modeset, and generally everywhere.

v2: addressing comments by Ville:
 - rename the dsi get config function to hsw_get_dsi_transcoder_state
 - rebase onto the higher level split of pipe/transcoder functions
 - use more has_dsi_encoder as we can now because of the above,
   with no need to look at the transcoder so much
 - rename IS_DSI_TRANSCODER to transcoder_is_dsi
 - use the above a bit more instead of comparing to < TRANSCODER_EDP

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/299740536b7941e31b2744f3ce34f7afe936a771.1458313400.git.jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 8727746..efca534 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -127,6 +127,8 @@
 	TRANSCODER_B,
 	TRANSCODER_C,
 	TRANSCODER_EDP,
+	TRANSCODER_DSI_A,
+	TRANSCODER_DSI_C,
 	I915_MAX_TRANSCODERS
 };
 
@@ -141,11 +143,20 @@
 		return "C";
 	case TRANSCODER_EDP:
 		return "EDP";
+	case TRANSCODER_DSI_A:
+		return "DSI A";
+	case TRANSCODER_DSI_C:
+		return "DSI C";
 	default:
 		return "<invalid>";
 	}
 }
 
+static inline bool transcoder_is_dsi(enum transcoder transcoder)
+{
+	return transcoder == TRANSCODER_DSI_A || transcoder == TRANSCODER_DSI_C;
+}
+
 /*
  * I915_MAX_PLANES in the enum below is the maximum (across all platforms)
  * number of planes per CRTC.  Not all platforms really have this many planes,
@@ -196,6 +207,8 @@
 	POWER_DOMAIN_TRANSCODER_B,
 	POWER_DOMAIN_TRANSCODER_C,
 	POWER_DOMAIN_TRANSCODER_EDP,
+	POWER_DOMAIN_TRANSCODER_DSI_A,
+	POWER_DOMAIN_TRANSCODER_DSI_C,
 	POWER_DOMAIN_PORT_DDI_A_LANES,
 	POWER_DOMAIN_PORT_DDI_B_LANES,
 	POWER_DOMAIN_PORT_DDI_C_LANES,