powerpc: convert makefiles to Kbuild style

Note:
arch/powerpc/cpu/mpc8260/Makefile is originally like follows:

    ---<snip>---
    START   = start.o kgdb.o
    COBJS   = traps.o serial_smc.o serial_scc.o cpu.o cpu_init.o speed.o \
    ---<snip>---
    COBJS-$(CONFIG_ETHER_ON_SCC) = ether_scc.o
    ---<snip>---
    $(LIB): $(OBJS)
            $(call cmd_link_o_target, $(OBJS) $(obj)kgdb.o)

The link rule `$(call cmd_link_o_target, $(OBJS) $(obj)kgdb.o)'
is weird.
kbdg.o is not included in $(OBJS) but linked into $(LIB)
and $(LIB) is not dependent on kgdb.o.
(Broken dependency tracking)

So,
    START   = start.o kgdb.o
shoud have been
    START   = start.o
    SOBJS   = kgdb.o

That is why this commit adds kgdb.o to obj-y, not to extra-y.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Stefan Roese <sr@denx.de>
diff --git a/arch/powerpc/cpu/mpc8xxx/Makefile b/arch/powerpc/cpu/mpc8xxx/Makefile
index 3dc8e05..395fed1 100644
--- a/arch/powerpc/cpu/mpc8xxx/Makefile
+++ b/arch/powerpc/cpu/mpc8xxx/Makefile
@@ -6,10 +6,6 @@
 # Version 2 as published by the Free Software Foundation.
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib8xxx.o
-
 MINIMAL=
 
 ifdef CONFIG_SPL_BUILD
@@ -20,30 +16,18 @@
 
 ifdef MINIMAL
 
-COBJS-$(CONFIG_FSL_LAW) += law.o
+obj-$(CONFIG_FSL_LAW) += law.o
 
 else
 
 ifneq ($(CPU),mpc83xx)
-COBJS-y	+= cpu.o
+obj-y	+= cpu.o
 endif
 
-COBJS-$(CONFIG_OF_LIBFDT) += fdt.o
-COBJS-$(CONFIG_FSL_IFC) += fsl_ifc.o
-COBJS-$(CONFIG_FSL_LBC) += fsl_lbc.o
-COBJS-$(CONFIG_SYS_SRIO) += srio.o
-COBJS-$(CONFIG_FSL_LAW) += law.o
+obj-$(CONFIG_OF_LIBFDT) += fdt.o
+obj-$(CONFIG_FSL_IFC) += fsl_ifc.o
+obj-$(CONFIG_FSL_LBC) += fsl_lbc.o
+obj-$(CONFIG_SYS_SRIO) += srio.o
+obj-$(CONFIG_FSL_LAW) += law.o
 
 endif
-
-SRCS	:= $(START:.o=.S) $(SOBJS-y:.o=.S) $(COBJS-y:.o=.c)
-OBJS	:= $(addprefix $(obj),$(SOBJS-y) $(COBJS-y))
-
-all:	$(obj).depend $(LIB)
-
-$(LIB):	$(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend