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/spl/Makefile b/spl/Makefile
index ec09831..1e88d74 100644
--- a/spl/Makefile
+++ b/spl/Makefile
@@ -42,17 +42,10 @@
 START_PATH := $(CPUDIR)
 endif
 
-START := $(START_PATH)/start.o
-ifeq ($(CPU),x86)
-START += $(START_PATH)/start16.o
-START += $(START_PATH)/resetvec.o
-endif
-ifeq ($(CPU),ppc4xx)
-START += $(START_PATH)/resetvec.o
-endif
-ifeq ($(CPU),mpc85xx)
-START += $(START_PATH)/resetvec.o
-endif
+head-y := $(START_PATH)/start.o
+head-$(CONFIG_X86) += $(START_PATH)/start16.o $(START_PATH)/resetvec.o
+head-$(CONFIG_4xx) += $(START_PATH)/resetvec.o
+head-$(CONFIG_MPC85xx) += $(START_PATH)/resetvec.o
 
 LIBS-y += arch/$(ARCH)/lib/
 
@@ -105,7 +98,7 @@
 PLATFORM_LIBS := $(filter-out %/libgcc.o, $(filter-out -lgcc, $(PLATFORM_LIBS))) $(PLATFORM_LIBGCC)
 endif
 
-START := $(addprefix $(SPLTREE)/,$(START))
+START := $(addprefix $(SPLTREE)/,$(head-y))
 LIBS := $(addprefix $(SPLTREE)/,$(sort $(LIBS-y)))
 
 __START := $(subst $(obj),,$(START))