powerpc: remove redundant CPU definition

CONFIG_${CPU} is defined by Kconfig.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Stefan Roese <sr@denx.de>
diff --git a/arch/powerpc/cpu/ppc4xx/config.mk b/arch/powerpc/cpu/ppc4xx/config.mk
index a7253b2..f87c9dc 100644
--- a/arch/powerpc/cpu/ppc4xx/config.mk
+++ b/arch/powerpc/cpu/ppc4xx/config.mk
@@ -5,7 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-PLATFORM_CPPFLAGS += -DCONFIG_4xx -mstring -msoft-float
+PLATFORM_CPPFLAGS += -mstring -msoft-float
 
 cfg=$(srctree)/include/configs/$(CONFIG_SYS_CONFIG_NAME:"%"=%).h
 is440:=$(shell grep CONFIG_440 $(cfg))