drm/i915: wire up CRC interrupt for ilk/snb

We enable the interrupt unconditionally and only control it
through the enable bit in the CRC control register.

v2: Extract per-platform helpers to compute the register values.

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1292b40..2ea33ee 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1223,6 +1223,7 @@
 	INTEL_PIPE_CRC_SOURCE_PLANE1,
 	INTEL_PIPE_CRC_SOURCE_PLANE2,
 	INTEL_PIPE_CRC_SOURCE_PF,
+	INTEL_PIPE_CRC_SOURCE_PIPE,
 	INTEL_PIPE_CRC_SOURCE_MAX,
 };