Separate set context from av1_encode_block_intra

Add av1_set_txb_context to perform context setting.
This will make the code cleaner and facilitate
lv_map experiment implementation

Change-Id: Iea7e1e8ff6820e2c9cf72961adaa58346a7eca75
diff --git a/av1/encoder/encodemb.h b/av1/encoder/encodemb.h
index 96aa5b2..c3a0774 100644
--- a/av1/encoder/encodemb.h
+++ b/av1/encoder/encodemb.h
@@ -63,6 +63,10 @@
 
 void av1_subtract_plane(MACROBLOCK *x, BLOCK_SIZE bsize, int plane);
 
+void av1_set_txb_context(MACROBLOCK *x, int plane, int block,
+                         BLOCK_SIZE plane_bsize, TX_SIZE tx_size,
+                         ENTROPY_CONTEXT *a, ENTROPY_CONTEXT *l);
+
 void av1_encode_block_intra(int plane, int block, int blk_row, int blk_col,
                             BLOCK_SIZE plane_bsize, TX_SIZE tx_size, void *arg);