Refactor FDO support code to ensure arm64 can also be built with FDO.

Change-Id: I752c9f411b0a046a15c72b4837efc1fb0503b470
diff --git a/core/combo/TARGET_linux-arm64.mk b/core/combo/TARGET_linux-arm64.mk
index 02c4b99..f57f695 100644
--- a/core/combo/TARGET_linux-arm64.mk
+++ b/core/combo/TARGET_linux-arm64.mk
@@ -49,6 +49,7 @@
 endif
 
 include $(TARGET_ARCH_SPECIFIC_MAKEFILE)
+include $(BUILD_SYSTEM)/combo/fdo.mk
 
 # You can set TARGET_TOOLS_PREFIX to get gcc from somewhere else
 ifeq ($(strip $(TARGET_TOOLS_PREFIX)),)