Use 10 bits to represent adapt_scan probabilities

The performance drop slightly by using 10 bit probabilities.
lowres: -0.048%
midres: 0.007
hdres: -0.06

Change-Id: I5ba7b5607802d084a599b779e5745f88b31e2cbe

av1/common/entropy.h

@@ -414,7 +414,7 @@ static INLINE int get_entropy_context(TX_SIZE tx_size, const ENTROPY_CONTEXT *a,
 #define COEF_MAX_UPDATE_FACTOR_AFTER_KEY 128
 
 #if CONFIG_ADAPT_SCAN
-#define ADAPT_SCAN_PROB_PRECISION 16
+#define ADAPT_SCAN_PROB_PRECISION 10
 // 1/8 update rate
 #define ADAPT_SCAN_UPDATE_LOG_RATE 3
 #define ADAPT_SCAN_UPDATE_RATE \