drm/i915: Disable DC states around GMBUS on GLK

Prevent the DMC from destroying GMBUS transfers on GLK. GMBUS
lives in PG1 so DC off is all we need.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171208213739.16388-1-ville.syrjala@linux.intel.comReviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -1792,6 +1792,7 @@ void intel_display_power_put(struct drm_i915_private *dev_priv,
 	BIT_ULL(POWER_DOMAIN_GT_IRQ) |			\
 	BIT_ULL(POWER_DOMAIN_MODESET) |			\
 	BIT_ULL(POWER_DOMAIN_AUX_A) |			\
+	BIT_ULL(POWER_DOMAIN_GMBUS) |			\
 	BIT_ULL(POWER_DOMAIN_INIT))
 
 #define CNL_DISPLAY_POWERWELL_2_POWER_DOMAINS (		\