cmake: Relocate CONFIG_FILEOPTIONS default.

This is not an experiment. It is a build configuration
flag that enables usage of config files within aomenc
and some minor tweaks in av1/encoder/encoder.c.

Change-Id: I1ba148baa13372f06bb782b52962061630c7c760

build/cmake/aom_config_defaults.cmake

diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 4865394..889d030 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -84,6 +84,7 @@
 set(CONFIG_ACCOUNTING 0 CACHE NUMBER "Enables bit accounting.")
 set(CONFIG_ANALYZER 0 CACHE NUMBER "Enables bit stream analyzer.")
 set(CONFIG_COEFFICIENT_RANGE_CHECKING 0 CACHE NUMBER "Coefficient range check.")
+set(CONFIG_FILEOPTIONS 1 CACHE NUMBER "Enables encoder config file support.")
 set(CONFIG_INSPECTION 0 CACHE NUMBER "Enables bitstream inspection.")
 set(CONFIG_INTERNAL_STATS 0 CACHE NUMBER "Codec stats.")
 set(CONFIG_LOWBITDEPTH 0 CACHE NUMBER "Enables 8-bit optimized pipeline.")
@@ -98,4 +99,3 @@
 set(CONFIG_RD_DEBUG 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SIMPLE_LRUNIT 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_TRAILING_BITS 0 CACHE NUMBER "AV1 experiment flag.")
-set(CONFIG_FILEOPTIONS 1 CACHE NUMBER "AV1 config option flag.")