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/m68k/config.mk b/arch/m68k/config.mk
index 33b3d51..3b3a7e8 100644
--- a/arch/m68k/config.mk
+++ b/arch/m68k/config.mk
@@ -11,7 +11,7 @@
 
 CONFIG_STANDALONE_LOAD_ADDR ?= 0x20000
 
-PLATFORM_CPPFLAGS += -DCONFIG_M68K -D__M68K__
+PLATFORM_CPPFLAGS += -D__M68K__
 PLATFORM_LDFLAGS  += -n
 PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections
 PLATFORM_RELFLAGS += -ffixed-d7 -msep-data