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/intel_fbc.c

@@ -108,7 +108,7 @@ static void i8xx_fbc_deactivate(struct drm_i915_private *dev_priv)
 	I915_WRITE(FBC_CONTROL, fbc_ctl);
 
 	/* Wait for compressing bit to clear */
-	if (intel_wait_for_register(dev_priv,
+	if (intel_wait_for_register(&dev_priv->uncore,
 				    FBC_STATUS, FBC_STAT_COMPRESSING, 0,
 				    10)) {
 		DRM_DEBUG_KMS("FBC idle timed out\n");