mpc5121: add common post_word_load/store code

Add common post_word_load/post_word_store routines
for all mpc5121 boards. pdm360ng board POST support
added by subsequent patch needs them.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
diff --git a/arch/powerpc/cpu/mpc512x/Makefile b/arch/powerpc/cpu/mpc512x/Makefile
index 1719c66..9cfdb0f 100644
--- a/arch/powerpc/cpu/mpc512x/Makefile
+++ b/arch/powerpc/cpu/mpc512x/Makefile
@@ -29,6 +29,7 @@
 START	= start.o
 COBJS-y	:= cpu.o
 COBJS-y	+= traps.o
+COBJS-y += common.o
 COBJS-y += cpu_init.o
 COBJS-y += fixed_sdram.o
 COBJS-y += i2c.o