Segregate global motion related wrapper functions

Moved global motion related wrapper functions in
encodeframe.c into a newly created file 'global_motion_facade.c'.

Change-Id: I582fc043718eaaa1191625f8400c192862f54d30
diff --git a/av1/encoder/ethread.c b/av1/encoder/ethread.c
index 7bcf4be..c33d0c2 100644
--- a/av1/encoder/ethread.c
+++ b/av1/encoder/ethread.c
@@ -18,6 +18,7 @@
 #include "av1/encoder/firstpass.h"
 #endif
 #include "av1/encoder/global_motion.h"
+#include "av1/encoder/global_motion_facade.h"
 #include "av1/encoder/rdopt.h"
 #include "aom_dsp/aom_dsp_common.h"
 #include "av1/encoder/tpl_model.h"