drm/i915: wrap GTIMR changes

Just like the functions that touch DEIMR and SDEIMR, but for GTIMR.
The new functions contain a POSTING_READ(GTIMR) which was not present
at the 2 callers inside i915_irq.c.

The implementation is based on ibx_display_interrupt_update.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 01455aa..a846206 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -778,5 +778,8 @@
 extern void hsw_disable_lcpll(struct drm_i915_private *dev_priv,
 			      bool switch_to_fclk, bool allow_power_down);
 extern void hsw_restore_lcpll(struct drm_i915_private *dev_priv);
+extern void ilk_enable_gt_irq(struct drm_i915_private *dev_priv, uint32_t mask);
+extern void ilk_disable_gt_irq(struct drm_i915_private *dev_priv,
+			       uint32_t mask);
 
 #endif /* __INTEL_DRV_H__ */