intel: add a command buffer scratch bo

It is owned by intel_dev so that all command buffers can share it.  Will be
used for workarounds.
diff --git a/icd/intel/dev.c b/icd/intel/dev.c
index 407c531..3613f54 100644
--- a/icd/intel/dev.c
+++ b/icd/intel/dev.c
@@ -98,6 +98,13 @@
         return XGL_ERROR_UNKNOWN;
     }
 
+    dev->cmd_scratch_bo = intel_winsys_alloc_buffer(dev->winsys,
+            "command buffer scratch", 4096, INTEL_DOMAIN_INSTRUCTION);
+    if (!dev->cmd_scratch_bo) {
+        intel_dev_destroy(dev);
+        return XGL_ERROR_OUT_OF_GPU_MEMORY;
+    }
+
     ret = dev_create_queues(dev, info->pRequestedQueues,
             info->queueRecordCount);
     if (ret != XGL_SUCCESS) {
@@ -137,6 +144,9 @@
             intel_queue_destroy(dev->queues[i]);
     }
 
+    if (dev->cmd_scratch_bo)
+        intel_bo_unreference(dev->cmd_scratch_bo);
+
     if (dev->winsys)
         intel_winsys_destroy(dev->winsys);