board: arm: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Cc: Andreas Bießmann <andreas.devel@googlemail.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Prafulla Wadaskar <prafulla@marvell.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Vipin Kumar <vipin.kumar@st.com>
Cc: Tom Warren <twarren@nvidia.com>
Cc: Tom Rini <trini@ti.com>
diff --git a/board/samsung/smdk5250/Makefile b/board/samsung/smdk5250/Makefile
index 0463079..6a58655 100644
--- a/board/samsung/smdk5250/Makefile
+++ b/board/samsung/smdk5250/Makefile
@@ -4,35 +4,12 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)lib$(BOARD).o
-
-COBJS	+= smdk5250_spl.o
+obj-y	+= smdk5250_spl.o
 
 ifndef CONFIG_SPL_BUILD
 ifdef CONFIG_OF_CONTROL
-COBJS	+= exynos5-dt.o
+obj-y	+= exynos5-dt.o
 else
-COBJS	+= smdk5250.o
+obj-y	+= smdk5250.o
 endif
 endif
-
-SRCS	:= $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS))
-
-ALL	:= $(obj).depend $(LIB)
-
-all:	$(ALL)
-
-$(LIB):	$(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################