drm/i915: load boot context at driver init time

According to the bspec for MBCTL:

Driver must set bit in the following scenarios:
  - to realod teh h/w boot context every time it gets loaded through OS
  - after an FLR clears the register (BIOS won't run afterwards)

References: https://bugs.freedesktop.org/show_bug.cgi?id=50237
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -3363,6 +3363,9 @@ static void gen6_init_clock_gating(struct drm_device *dev)
 		   ILK_DPARB_CLK_GATE  |
 		   ILK_DPFD_CLK_GATE);
 
+	I915_WRITE(GEN6_MBCTL, I915_READ(GEN6_MBCTL) |
+		   GEN6_MBCTL_ENABLE_BOOT_FETCH);
+
 	for_each_pipe(pipe) {
 		I915_WRITE(DSPCNTR(pipe),
 			   I915_READ(DSPCNTR(pipe)) |
@@ -3441,6 +3444,9 @@ static void ivybridge_init_clock_gating(struct drm_device *dev)
 		intel_flush_display_plane(dev_priv, pipe);
 	}
 
+	I915_WRITE(GEN6_MBCTL, I915_READ(GEN6_MBCTL) |
+		   GEN6_MBCTL_ENABLE_BOOT_FETCH);
+
 	gen7_setup_fixed_func_scheduler(dev_priv);
 
 	/* WaDisable4x2SubspanOptimization */
@@ -3484,6 +3490,9 @@ static void valleyview_init_clock_gating(struct drm_device *dev)
 		   I915_READ(GEN7_SQ_CHICKEN_MBCUNIT_CONFIG) |
 		   GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB);
 
+	I915_WRITE(GEN6_MBCTL, I915_READ(GEN6_MBCTL) |
+		   GEN6_MBCTL_ENABLE_BOOT_FETCH);
+
 
 	/* According to the BSpec vol1g, bit 12 (RCPBUNIT) clock
 	 * gating disable must be set.  Failure to set it results in