Add config flag for monochrome only video support

Change-Id: I04560ea2893087b0485133d7a123ceb594d9d0d2

build/cmake/aom_config_defaults.cmake

@@ -165,6 +165,7 @@ set(CONFIG_LV_MAP 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_MASKED_TX 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_MAX_TILE 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_MFMV 0 CACHE NUMBER "AV1 experiment flag.")
+set(CONFIG_MONO_VIDEO 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_MRC_TX 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_MV_COMPRESS 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_NCOBMC 0 CACHE NUMBER "AV1 experiment flag.")

configure

@@ -338,6 +338,7 @@ EXPERIMENT_LIST="
     simple_bwd_adapt
     eob_first
     eighth_pel_mv_only
+    mono_video
 "
 CONFIG_LIST="
     dependency_tracking