Update MV cdf stats per superblock

Adds a control and parameter for MV CDF updates.
Mv updates are enabled by default to be at a per
superblock level leading to an improvement in BDRATE
by -0.1 to -0.15%.
Slowdown by instruction count is ~ 1%

STATS_CHANGED

Change-Id: I549aace428724cb6f50d3d33c3e19c23b77283d3
diff --git a/apps/aomenc.c b/apps/aomenc.c
index ef3bd17..7b01af2 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -591,6 +591,10 @@
     ARG_DEF(NULL, "mode-cost-upd-freq", 1,
             "Update freq for mode costs"
             "0: SB, 1: SB Row per Tile, 2: Tile");
+static const arg_def_t mv_cost_upd_freq =
+    ARG_DEF(NULL, "mv-cost-upd-freq", 1,
+            "Update freq for mv costs"
+            "0: SB, 1: SB Row per Tile, 2: Tile");
 #if CONFIG_DIST_8X8
 static const arg_def_t enable_dist_8x8 =
     ARG_DEF(NULL, "enable-dist-8x8", 1,
@@ -857,6 +861,7 @@
                                        &quant_b_adapt,
                                        &coeff_cost_upd_freq,
                                        &mode_cost_upd_freq,
+                                       &mv_cost_upd_freq,
 #if CONFIG_DIST_8X8
                                        &enable_dist_8x8,
 #endif
@@ -961,6 +966,7 @@
                                         AV1E_SET_QUANT_B_ADAPT,
                                         AV1E_SET_COEFF_COST_UPD_FREQ,
                                         AV1E_SET_MODE_COST_UPD_FREQ,
+                                        AV1E_SET_MV_COST_UPD_FREQ,
 #if CONFIG_DIST_8X8
                                         AV1E_SET_ENABLE_DIST_8X8,
 #endif