arm926ejs: convert makefiles to Kbuild style

Note1:
In arch/arm/cpu/arm926ejs/spear/Makefile
START := start.o
was changed
extra-$(CONFIG_SPL_BUILD) := start.o
because spear/start.o is only used for SPL.

Note2:
START := start.o
was missing from arch/arm/cpu/arm926ejs/mxs/Makefile.
This commit simply adds
extra-$(CONFIG_SPL_BUILD) := start.o

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/arch/arm/cpu/arm926ejs/spear/Makefile b/arch/arm/cpu/arm926ejs/spear/Makefile
index 3006cd6..3f190bc 100644
--- a/arch/arm/cpu/arm926ejs/spear/Makefile
+++ b/arch/arm/cpu/arm926ejs/spear/Makefile
@@ -5,37 +5,17 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib$(SOC).o
-
-COBJS-y	:= cpu.o \
+obj-y	:= cpu.o \
 	   reset.o \
 	   timer.o
 
 ifdef CONFIG_SPL_BUILD
-COBJS-y	+= spl.o spl_boot.o
-COBJS-$(CONFIG_SPEAR600) += spear600.o
-COBJS-$(CONFIG_DDR_MT47H64M16) += spr600_mt47h64m16_3_333_cl5_psync.o
-COBJS-$(CONFIG_DDR_MT47H32M16) += spr600_mt47h32m16_333_cl5_psync.o
-COBJS-$(CONFIG_DDR_MT47H32M16) += spr600_mt47h32m16_37e_166_cl4_sync.o
-COBJS-$(CONFIG_DDR_MT47H128M8) += spr600_mt47h128m8_3_266_cl5_async.o
+obj-y	+= spl.o spl_boot.o
+obj-$(CONFIG_SPEAR600) += spear600.o
+obj-$(CONFIG_DDR_MT47H64M16) += spr600_mt47h64m16_3_333_cl5_psync.o
+obj-$(CONFIG_DDR_MT47H32M16) += spr600_mt47h32m16_333_cl5_psync.o
+obj-$(CONFIG_DDR_MT47H32M16) += spr600_mt47h32m16_37e_166_cl4_sync.o
+obj-$(CONFIG_DDR_MT47H128M8) += spr600_mt47h128m8_3_266_cl5_async.o
 endif
 
-SRCS	:= $(START:.o=.S) $(COBJS-y:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS-y))
-START	:= $(addprefix $(obj),$(START))
-
-all:	$(obj).depend $(LIB)
-
-$(LIB):	$(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+extra-$(CONFIG_SPL_BUILD) := start.o