Adds config opt for highbitdepth + misc. vpx

Adds config parameter vp9_highbitdepth, to support highbitdepth profiles.
Also includes most vpx level high bit-depth functions. However
encode/decode in the highbitdepth profiles will not work until
the rest of the code is in place.

Change-Id: I34c53b253c38873611057a6cbc89a1361b8985a6
diff --git a/vp8/vp8_cx_iface.c b/vp8/vp8_cx_iface.c
index 5be645c..4237efc 100644
--- a/vp8/vp8_cx_iface.c
+++ b/vp8/vp8_cx_iface.c
@@ -1244,6 +1244,9 @@
 
         320,                /* g_width */
         240,                /* g_height */
+        VPX_BITS_8,         /* g_bit_depth */
+        8,                  /* g_input_bit_depth */
+
         {1, 30},            /* g_timebase */
 
         0,                  /* g_error_resilient */