drm/i915: switch intel_wait_for_register to uncore

The intel_uncore structure is the owner of register access, so
subclass the function to it.

While at it, use a local uncore var and switch to the new read/write
functions where it makes sense.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190325214940.23632-9-daniele.ceraolospurio@intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -2687,7 +2687,7 @@ int vlv_force_gfx_clock(struct drm_i915_private *dev_priv, bool force_on)
 	if (!force_on)
 		return 0;
 
-	err = intel_wait_for_register(dev_priv,
+	err = intel_wait_for_register(&dev_priv->uncore,
 				      VLV_GTLC_SURVIVABILITY_REG,
 				      VLV_GFX_CLK_STATUS_BIT,
 				      VLV_GFX_CLK_STATUS_BIT,