Makefile: Select objects by CONFIG_ rather than $(ARCH) or $(CPU)

Convert like follows:

 CPU mpc83xx  -> CONFIG_MPC83xx
 CPU mpc85xx  -> CONFIG_MPC85xx
 CPU mpc86xx  -> CONFIG_MPC86xx
 CPU mpc5xxx  -> CONFIG_MPC5xxx
 CPU mpc8xx   -> CONFIG_8xx
 CPU mpc8260  -> CONFIG_8260
 CPU ppc4xx   -> CONFIG_4xx
 CPU x86      -> CONFIG_X86
 ARCH x86     -> CONFIG_X86
 ARCH powerpc -> CONFIG_PPC

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/arch/powerpc/cpu/mpc8xxx/Makefile b/arch/powerpc/cpu/mpc8xxx/Makefile
index f66ee2e..e95539e 100644
--- a/arch/powerpc/cpu/mpc8xxx/Makefile
+++ b/arch/powerpc/cpu/mpc8xxx/Makefile
@@ -19,10 +19,8 @@
 obj-$(CONFIG_FSL_LAW) += law.o
 
 else
-
-ifneq ($(CPU),mpc83xx)
-obj-y	+= cpu.o
-endif
+obj-$(CONFIG_MPC85xx) += cpu.o
+obj-$(CONFIG_MPC86xx) += cpu.o
 
 obj-$(CONFIG_OF_LIBFDT) += fdt.o
 obj-$(CONFIG_FSL_LBC) += fsl_lbc.o