PowerPC: merge commonly-defined flags

PLATFORM_RELFLAGS += -meabi
PLATFORM_CPPFLAGS += -ffixed-r2
were defined in all arch/powerpc/${CPU}/config.mk.

This commit moves them to arch/powerpc/config.mk.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/arch/powerpc/cpu/ppc4xx/config.mk b/arch/powerpc/cpu/ppc4xx/config.mk
index c2b0f9a..71c2a6c 100644
--- a/arch/powerpc/cpu/ppc4xx/config.mk
+++ b/arch/powerpc/cpu/ppc4xx/config.mk
@@ -5,8 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-PLATFORM_RELFLAGS += -meabi
-PLATFORM_CPPFLAGS += -DCONFIG_4xx -ffixed-r2 -mstring -msoft-float
+PLATFORM_CPPFLAGS += -DCONFIG_4xx -mstring -msoft-float
 
 cfg=$(shell grep configs $(OBJTREE)/include/config.h | sed 's/.*<\(configs.*\)>/\1/')
 is440:=$(shell grep CONFIG_440 $(TOPDIR)/include/$(cfg))