intel: add INTEL_DEBUG env var to help debugging

INTEL_DEBUG=batch to enable bo decoding on cmdbuf submission
diff --git a/icd/intel/queue.c b/icd/intel/queue.c
index 31a92e3..e408700 100644
--- a/icd/intel/queue.c
+++ b/icd/intel/queue.c
@@ -81,7 +81,8 @@
 
     bo = intel_cmd_get_batch(cmd, &used);
 
-    intel_winsys_decode_bo(winsys, bo, used);
+    if (intel_debug & INTEL_DEBUG_BATCH)
+        intel_winsys_decode_bo(winsys, bo, used);
 
     err = intel_winsys_submit_bo(winsys, queue->ring, bo, used, 0);