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/mpc83xx/Makefile b/arch/powerpc/cpu/mpc83xx/Makefile
index 6341cd4..b7142f0 100644
--- a/arch/powerpc/cpu/mpc83xx/Makefile
+++ b/arch/powerpc/cpu/mpc83xx/Makefile
@@ -7,10 +7,6 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib$(CPU).o
-
 MINIMAL=
 
 ifdef CONFIG_SPL_BUILD
@@ -19,48 +15,39 @@
 endif
 endif
 
-START	= start.o
+extra-y	= start.o
 
 ifdef MINIMAL
 
-COBJS-y	+= spl_minimal.o
+obj-y	+= spl_minimal.o
 
 else
 
-COBJS-y += traps.o
-COBJS-y += cpu.o
-COBJS-y += cpu_init.o
-COBJS-y += speed.o
-COBJS-y += interrupts.o
-COBJS-y += ecc.o
-COBJS-$(CONFIG_QE) += qe_io.o
-COBJS-$(CONFIG_FSL_SERDES) += serdes.o
-COBJS-$(CONFIG_PCI) += pci.o
-COBJS-$(CONFIG_PCIE) += pcie.o
-COBJS-$(CONFIG_OF_LIBFDT) += fdt.o
+obj-y += traps.o
+obj-y += cpu.o
+obj-y += cpu_init.o
+obj-y += speed.o
+obj-y += interrupts.o
+obj-y += ecc.o
+obj-$(CONFIG_QE) += qe_io.o
+obj-$(CONFIG_FSL_SERDES) += serdes.o
+obj-$(CONFIG_PCI) += pci.o
+obj-$(CONFIG_PCIE) += pcie.o
+obj-$(CONFIG_OF_LIBFDT) += fdt.o
 
 # Stub implementations of cache management functions for USB
-COBJS-y += cache.o
+obj-y += cache.o
 
 ifdef CONFIG_FSL_DDR2
-COBJS_LN-$(CONFIG_MPC8349) += ddr-gen2.o
+obj-$(CONFIG_MPC8349) += ddr-gen2.o
+SRCS += $(obj)ddr-gen2.c
 else
-COBJS-y += spd_sdram.o
+obj-y += spd_sdram.o
 endif
-COBJS-$(CONFIG_FSL_DDR2) += law.o
+obj-$(CONFIG_FSL_DDR2) += law.o
 
 endif # not minimal
 
-COBJS	:= $(COBJS-y)
-SRCS	:= $(START:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c) $(addprefix $(obj),$(COBJS_LN-y:.o=.c))
-OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS) $(COBJS_LN-y))
-START	:= $(addprefix $(obj),$(START))
-
-all:	$(obj).depend $(START) $(LIB)
-
-$(LIB):	$(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
 $(obj)ddr-gen1.c:
 	ln -sf $(SRCTREE)/arch/powerpc/cpu/mpc85xx/ddr-gen1.c $(obj)ddr-gen1.c
 
@@ -69,12 +56,3 @@
 
 $(obj)ddr-gen3.c:
 	ln -sf $(SRCTREE)/arch/powerpc/cpu/mpc85xx/ddr-gen3.c $(obj)ddr-gen3.c
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################