Allow to disable the probability update

Added the function of allowing to disable the probability update while
needed. This would be needed while encoding in multiple tiles, and
enabling/disabling probability update can be set separately for every
individual tile.

Change-Id: Ic3c64e6cebac89c483d48b874761bd2e902d81e6

av1/encoder/encoder.h

diff --git a/av1/encoder/encoder.h b/av1/encoder/encoder.h
index ff978a2..075b07d 100644
--- a/av1/encoder/encoder.h
+++ b/av1/encoder/encoder.h
@@ -320,6 +320,7 @@
   CFL_CTX cfl;
 #endif
   DECLARE_ALIGNED(16, FRAME_CONTEXT, tctx);
+  uint8_t allow_update_cdf;
 } TileDataEnc;
 
 typedef struct RD_COUNTS {