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/mpc85xx/config.mk b/arch/powerpc/cpu/mpc85xx/config.mk
index 9eef539..72c964c 100644
--- a/arch/powerpc/cpu/mpc85xx/config.mk
+++ b/arch/powerpc/cpu/mpc85xx/config.mk
@@ -5,13 +5,10 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-PLATFORM_RELFLAGS += -meabi
-
-PLATFORM_CPPFLAGS += -ffixed-r2 -Wa,-me500 -msoft-float -mno-string
+PLATFORM_CPPFLAGS += -Wa,-me500 -msoft-float -mno-string
 
 # -mspe=yes is needed to have -mno-spe accepted by a buggy GCC;
 # see "[PATCH,rs6000] make -mno-spe work as expected" on
 # http://gcc.gnu.org/ml/gcc-patches/2008-04/msg00311.html
-PF_CPPFLAGS_SPE := $(call cc-option,-mspe=yes) \
+PLATFORM_CPPFLAGS += $(call cc-option,-mspe=yes) \
 		   $(call cc-option,-mno-spe)
-PLATFORM_CPPFLAGS += $(PF_CPPFLAGS_SPE)