Move inter filter defs to vp9_filter.h

Add comments on the use case of these definitions. Further reduce
the scope of header file in vp9_context_tree.h.

Change-Id: Ic4a7638e838d0ac441b64abfc56e57354c059d75

vp9/common/vp9_entropymode.h

@@ -20,8 +20,6 @@ extern "C" {
 #endif
 
 #define TX_SIZE_CONTEXTS 2
-#define SWITCHABLE_FILTERS 3   // number of switchable filters
-#define SWITCHABLE_FILTER_CONTEXTS (SWITCHABLE_FILTERS + 1)
 
 struct VP9Common;
 

vp9/common/vp9_filter.h

@@ -35,6 +35,13 @@ typedef enum {
   SWITCHABLE = 4  /* should be the last one */
 } INTERP_FILTER;
 
+// Number of switchable filters
+#define SWITCHABLE_FILTERS 3
+
+// The codec can operate in four possible inter prediction filter mode:
+// 8-tap, 8-tap-smooth, 8-tap-sharp, and switching between the three.
+#define SWITCHABLE_FILTER_CONTEXTS (SWITCHABLE_FILTERS + 1)
+
 typedef int16_t InterpKernel[SUBPEL_TAPS];
 
 const InterpKernel *vp9_get_interp_kernel(INTERP_FILTER filter);

vp9/encoder/vp9_context_tree.h

@@ -11,9 +11,10 @@
 #ifndef VP9_ENCODER_VP9_CONTEXT_TREE_H_
 #define VP9_ENCODER_VP9_CONTEXT_TREE_H_
 
-#include "vp9/common/vp9_entropymode.h"
+#include "vp9/common/vp9_blockd.h"
 
 struct VP9_COMP;
+struct VP9Common;
 
 // Structure to hold snapshot of coding context during the mode picking process
 typedef struct {