Add encoder options for reduced tx type set

Adds a command line flag and control option for a reduced transform
type set.

Change-Id: I392c4f7f9b24f7d0451d1417fe680896ec2cf447
diff --git a/av1/encoder/encoder.h b/av1/encoder/encoder.h
index 3fbb0ce..41cd62e 100644
--- a/av1/encoder/encoder.h
+++ b/av1/encoder/encoder.h
@@ -341,6 +341,7 @@
 
   unsigned int chroma_subsampling_x;
   unsigned int chroma_subsampling_y;
+  int reduced_tx_type_set;
 } AV1EncoderConfig;
 
 static INLINE int is_lossless_requested(const AV1EncoderConfig *cfg) {