kconfig: delete redundant CONFIG_${ARCH} definition

CONFIG_${ARCH} is defined by Kconfig.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index c3b8289..c339e6d 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -22,7 +22,7 @@
 # Support generic board on ARM
 __HAVE_ARCH_GENERIC_BOARD := y
 
-PLATFORM_CPPFLAGS += -DCONFIG_ARM -D__ARM__
+PLATFORM_CPPFLAGS += -D__ARM__
 
 # Choose between ARM/Thumb instruction sets
 ifeq ($(CONFIG_SYS_THUMB_BUILD),y)