drm/i915: Move legacy breadcrumb out of the reserved status page area

Addresses in the hardware status page below index 0x20 are reserved for use
by the hardware. The legacy breadcrumb was sitting at index 5. Move it to
index 0x21, and make sure everyone uses the defined value instead of
hard-coded constants.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4afbadb..ef1c0b8 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -608,8 +608,9 @@
  * The area from dword 0x20 to 0x3ff is available for driver usage.
  */
 #define READ_HWSP(dev_priv, reg)  (((volatile u32*)(dev_priv->hw_status_page))[reg])
-#define READ_BREADCRUMB(dev_priv) READ_HWSP(dev_priv, 5)
+#define READ_BREADCRUMB(dev_priv) READ_HWSP(dev_priv, I915_BREADCRUMB_INDEX)
 #define I915_GEM_HWS_INDEX		0x20
+#define I915_BREADCRUMB_INDEX		0x21
 
 extern int i915_wait_ring(struct drm_device * dev, int n, const char *caller);