arm: Centralize fixed register logic

When building for ARM64, we need to pass -ffixed-x18 and otherwise pass
-ffixed-r9. Rather than having this logic in two places, we can do this
once in arch/arm/config.mk. Further, while gcc will ignore being passed
both -ffixed-r9 and -ffixed-x18 and simply use -ffixed-x18, clang will
note that -ffixed-r9 is not used. Remove this duplication to also remove
the warning.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index bf781f1..5530d02 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -3,7 +3,13 @@
 # (C) Copyright 2000-2002
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 
-CFLAGS_NON_EFI := -fno-pic -ffixed-r9 -ffunction-sections -fdata-sections \
+ifeq ($(CONFIG_ARM64),y)
+FIXED_REG := -ffixed-x18
+else
+FIXED_REG := -ffixed-r9
+endif
+
+CFLAGS_NON_EFI := -fno-pic $(FIXED_REG) -ffunction-sections -fdata-sections \
 		  -fstack-protector-strong
 CFLAGS_EFI := -fpic -fshort-wchar
 
@@ -15,7 +21,7 @@
 PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections
 endif
 
-PLATFORM_RELFLAGS += -fno-common -ffixed-r9
+PLATFORM_RELFLAGS += -fno-common $(FIXED_REG)
 PLATFORM_RELFLAGS += $(call cc-option, -msoft-float) \
 		     $(call cc-option,-mgeneral-regs-only) \
       $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,))