drm/i915: Replace DRM_DEBUG with DRM_DEBUG_DRIVER

Replace the DRM_DEBUG with DRM_DEBUG_DRIVER in generic i915 driver.
Then the debug info can be obtained by adding the boot option of
"drm.debug=0x02".

At the same time the debug info in increase/decrease clock is also
printed by using DRM_DEBUG_DRIVER instead of DRM_DEBUG_KMS.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
index 200e398..0c8df96 100644
--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
@@ -121,7 +121,7 @@
 				     0,   pcibios_align_resource,
 				     dev_priv->bridge_dev);
 	if (ret) {
-		DRM_DEBUG("failed bus alloc: %d\n", ret);
+		DRM_DEBUG_DRIVER("failed bus alloc: %d\n", ret);
 		dev_priv->mch_res.start = 0;
 		goto out;
 	}