drm/i915: Use msleep instead of mdelay during wait_vblank_off

Avoid a potentially long busy-wait if we not in the process of
atomically switching to the kdb console.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 6c6b897..e5f2a61 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -49,6 +49,13 @@
 #define wait_for(COND, MS) _wait_for(COND, MS, 1)
 #define wait_for_atomic(COND, MS) _wait_for(COND, MS, 0)
 
+#define MSLEEP(x) do { \
+	if (in_dbg_master()) \
+	       	mdelay(x); \
+	else \
+		msleep(x); \
+} while(0)
+
 #define KHz(x) (1000*x)
 #define MHz(x) KHz(1000*x)