drm/i915/bxt: fix dsi hw state pipe readout

BXT isn't as limited as BYT and CHT regarding DSI pipes and ports.

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/8bea85b86aaf7a15f854a656bf8d3208a3afe0bd.1458070700.git.jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 85ceec6..d4a298f 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -8144,6 +8144,7 @@
 #define  READ_REQUEST_PRIORITY_HIGH			(3 << 3)
 #define  RGB_FLIP_TO_BGR				(1 << 2)
 
+#define  BXT_PIPE_SELECT_SHIFT				7
 #define  BXT_PIPE_SELECT_MASK				(7 << 7)
 #define  BXT_PIPE_SELECT(pipe)				((pipe) << 7)