Adds macros for new encoder controls

To aid version management for integration with ffmpeg by use
of:
  #ifdef VPX_CTRL_<CTRL_ID>
    ...
  #endif

Change-Id: If550e06de4d3aa3685881f312ce6a86fa9de083b

vpx/vp8cx.h

diff --git a/vpx/vp8cx.h b/vpx/vp8cx.h
index bdbb1b2..013c67a 100644
--- a/vpx/vp8cx.h
+++ b/vpx/vp8cx.h
@@ -733,8 +733,10 @@
 VPX_CTRL_USE_TYPE(VP9E_SET_COLOR_SPACE, int)
 
 VPX_CTRL_USE_TYPE(VP9E_SET_MIN_GF_INTERVAL,  unsigned int)
+#define VPX_CTRL_VP9E_SET_MIN_GF_INTERVAL
 
 VPX_CTRL_USE_TYPE(VP9E_SET_MAX_GF_INTERVAL,  unsigned int)
+#define VPX_CTRL_VP9E_SET_MAX_GF_INTERVAL
 
 VPX_CTRL_USE_TYPE(VP9E_GET_ACTIVEMAP, vpx_active_map_t *)
 /*! @} - end defgroup vp8_encoder */