intel: enable HiZ on Gen7+

The support is restricted to Gen7+.  To support HiZ on Gen6, we need to
perform manual combined/separated stencil resolves and that may hurt the
performance instead.

Also, we do not support fast depth clears.  xglSetFastClearDepth() will be
removed in a later xgl.h revision.
diff --git a/icd/intel/intel.h b/icd/intel/intel.h
index 11b69e2..774abf3 100644
--- a/icd/intel/intel.h
+++ b/icd/intel/intel.h
@@ -64,7 +64,8 @@
 
     INTEL_DEBUG_NOHW        = 1 << 20,
     INTEL_DEBUG_NOCACHE     = 1 << 21,
-    INTEL_DEBUG_HANG        = 1 << 22,
+    INTEL_DEBUG_NOHIZ       = 1 << 22,
+    INTEL_DEBUG_HANG        = 1 << 23,
 };
 
 extern int intel_debug;