arm: prevent using movt/movw address loads

The movt/movw instruction can be used to hardcode an
memory location in the instruction itself. The linker
starts complaining about this if the compiler decides
to do so: "relocation R_ARM_MOVW_ABS_NC against `a local
symbol' can not be used" and it is not support by U-boot
as well. Prevent their use by requiring word relocations.
This allows u-boot to be build at other optimalization
levels then -Os.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Cc: TigerLiu@viatech.com.cn
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Acked-by: Simon Glass <sjg@chromium.org>

arch/arm/config.mk

@@ -94,7 +94,11 @@ PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
 endif
 endif
 
-# check that only R_ARM_RELATIVE relocations are generated
 ifneq ($(CONFIG_SPL_BUILD),y)
-ALL-y	+= checkarmreloc
+# Check that only R_ARM_RELATIVE relocations are generated.
+ALL-y += checkarmreloc
+# The movt / movw can hardcode 16 bit parts of the addresses in the
+# instruction. Relocation is not supported for that case, so disable
+# such usage by requiring word relocations.
+PLATFORM_CPPFLAGS += $(call cc-option, -mword-relocations)
 endif