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/x86/cpu/config.mk b/arch/x86/cpu/config.mk
index 4b2c873..f7b01d3 100644
--- a/arch/x86/cpu/config.mk
+++ b/arch/x86/cpu/config.mk
@@ -7,7 +7,7 @@
 
 CROSS_COMPILE ?= i386-linux-
 
-PLATFORM_CPPFLAGS += -DCONFIG_X86 -D__I386__ -Werror
+PLATFORM_CPPFLAGS += -D__I386__ -Werror
 
 # DO NOT MODIFY THE FOLLOWING UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!
 LDPPFLAGS += -DRESET_SEG_START=0xffff0000