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/nds32/config.mk b/arch/nds32/config.mk
index 1024852..5ac9f90 100644
--- a/arch/nds32/config.mk
+++ b/arch/nds32/config.mk
@@ -17,6 +17,6 @@
 
 PLATFORM_RELFLAGS	+= -fno-strict-aliasing -fno-common -mrelax
 PLATFORM_RELFLAGS	+= -gdwarf-2
-PLATFORM_CPPFLAGS	+= -DCONFIG_NDS32 -D__nds32__ -G0 -ffixed-10 -fpie
+PLATFORM_CPPFLAGS	+= -D__nds32__ -G0 -ffixed-10 -fpie
 
 LDFLAGS_u-boot		= --gc-sections --relax