Add ref buffer management state enum

Change-Id: I809a5177ec0fb0b79f61b65390b6772c926c2743
diff --git a/av1/encoder/ratectrl.h b/av1/encoder/ratectrl.h
index 0a3a1dd..42b276c 100644
--- a/av1/encoder/ratectrl.h
+++ b/av1/encoder/ratectrl.h
@@ -76,6 +76,8 @@
   FRAME_UPDATE_TYPES
 } UENUM1BYTE(FRAME_UPDATE_TYPE);
 
+enum { REFBUF_RESET, REFBUF_UPDATE, REFBUF_STATES } UENUM1BYTE(REFBUF_STATE);
+
 typedef enum {
   NO_RESIZE = 0,
   DOWN_THREEFOUR = 1,  // From orig to 3/4.