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/at91/Makefile b/arch/arm/cpu/arm926ejs/at91/Makefile
index 9faec91..698a28d 100644
--- a/arch/arm/cpu/arm926ejs/at91/Makefile
+++ b/arch/arm/cpu/arm926ejs/at91/Makefile
@@ -5,46 +5,25 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib$(SOC).o
-
-COBJS-$(CONFIG_AT91CAP9)	+= at91cap9_devices.o
-COBJS-$(CONFIG_AT91SAM9260)	+= at91sam9260_devices.o
-COBJS-$(CONFIG_AT91SAM9G20)	+= at91sam9260_devices.o
-COBJS-$(CONFIG_AT91SAM9XE)	+= at91sam9260_devices.o
-COBJS-$(CONFIG_AT91SAM9261)	+= at91sam9261_devices.o
-COBJS-$(CONFIG_AT91SAM9G10)	+= at91sam9261_devices.o
-COBJS-$(CONFIG_AT91SAM9263)	+= at91sam9263_devices.o
-COBJS-$(CONFIG_AT91SAM9RL)	+= at91sam9rl_devices.o
-COBJS-$(CONFIG_AT91SAM9M10G45)	+= at91sam9m10g45_devices.o
-COBJS-$(CONFIG_AT91SAM9G45)	+= at91sam9m10g45_devices.o
-COBJS-$(CONFIG_AT91SAM9N12)	+= at91sam9n12_devices.o
-COBJS-$(CONFIG_AT91SAM9X5)	+= at91sam9x5_devices.o
-COBJS-$(CONFIG_AT91_EFLASH)	+= eflash.o
-COBJS-$(CONFIG_AT91_LED)	+= led.o
-COBJS-y += clock.o
-COBJS-y += cpu.o
-COBJS-y	+= reset.o
-COBJS-y	+= timer.o
+obj-$(CONFIG_AT91CAP9)	+= at91cap9_devices.o
+obj-$(CONFIG_AT91SAM9260)	+= at91sam9260_devices.o
+obj-$(CONFIG_AT91SAM9G20)	+= at91sam9260_devices.o
+obj-$(CONFIG_AT91SAM9XE)	+= at91sam9260_devices.o
+obj-$(CONFIG_AT91SAM9261)	+= at91sam9261_devices.o
+obj-$(CONFIG_AT91SAM9G10)	+= at91sam9261_devices.o
+obj-$(CONFIG_AT91SAM9263)	+= at91sam9263_devices.o
+obj-$(CONFIG_AT91SAM9RL)	+= at91sam9rl_devices.o
+obj-$(CONFIG_AT91SAM9M10G45)	+= at91sam9m10g45_devices.o
+obj-$(CONFIG_AT91SAM9G45)	+= at91sam9m10g45_devices.o
+obj-$(CONFIG_AT91SAM9N12)	+= at91sam9n12_devices.o
+obj-$(CONFIG_AT91SAM9X5)	+= at91sam9x5_devices.o
+obj-$(CONFIG_AT91_EFLASH)	+= eflash.o
+obj-$(CONFIG_AT91_LED)	+= led.o
+obj-y += clock.o
+obj-y += cpu.o
+obj-y	+= reset.o
+obj-y	+= timer.o
 
 ifndef CONFIG_SKIP_LOWLEVEL_INIT
-SOBJS-y	:= lowlevel_init.o
+obj-y	+= lowlevel_init.o
 endif
-
-SRCS    := $(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))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################