Turn on ref-adapt by default

This experiment of ref-adapt removes the option of COMPOUND_REFERENCE
from the frame level reference_mode setup, and hence removes 1 bit
in the frame header syntax. It now allows only SINGLE_REFERENCE or
REFERENCE_MODE_SELECT to specify in the frame header.

No noticeable coding performance impact has been observed.

Change-Id: I1bed64f927f31d396e8174a4f0c9119242bf0b5c

build/cmake/aom_config_defaults.cmake

@@ -172,7 +172,7 @@ set(CONFIG_RD_DEBUG 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_RECT_TX_EXT 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_RECT_TX_EXT_INTRA 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_REFERENCE_BUFFER 1 CACHE NUMBER "AV1 experiment flag.")
-set(CONFIG_REF_ADAPT 0 CACHE NUMBER "AV1 experiment flag.")
+set(CONFIG_REF_ADAPT 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SEGMENT_GLOBALMV 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SEGMENT_PRED_LAST 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SHORT_FILTER 1 CACHE NUMBER "AV1 experiment flag.")

configure

@@ -518,6 +518,7 @@ post_process_cmdline() {
     soft_enable filter_intra
     soft_enable ext_skip
     soft_enable frame_sign_bias
+    soft_enable ref_adapt
     soft_enable ext_warped_motion
     soft_enable horzonly_frame_superres