ARM: imx-common: convert makefiles to Kbuild style

Multiple targets are included in arch/arm/imx-common/Makefile
In order to refactor it,
we need to tweak Makefile and spl/Makefile.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/Makefile b/Makefile
index 1840dac..8fb35ce 100644
--- a/Makefile
+++ b/Makefile
@@ -416,6 +416,8 @@
 endif
 endif
 
+build := -f $(TOPDIR)/scripts/Makefile.build -C
+
 all:		$(ALL-y) $(SUBDIR_EXAMPLES)
 
 $(obj)u-boot.dtb:	checkdtc $(obj)u-boot
@@ -463,7 +465,7 @@
 		-d $< $@
 
 $(obj)u-boot.imx: $(obj)u-boot.bin depend
-		$(MAKE) -C $(SRCTREE)/arch/arm/imx-common $(OBJTREE)/u-boot.imx
+		$(MAKE) $(build) $(SRCTREE)/arch/arm/imx-common $(OBJTREE)/u-boot.imx
 
 $(obj)u-boot.kwb:       $(obj)u-boot.bin
 		$(obj)tools/mkimage -n $(CONFIG_SYS_KWD_CONFIG) -T kwbimage \
@@ -501,11 +503,11 @@
 		$(call SPL_PAD_APPEND,$<,$(obj)u-boot.bin,tpl/u-boot-tpl-pad.bin,$(CONFIG_TPL_PAD_TO))
 
 $(obj)u-boot-with-spl.imx: $(obj)spl/u-boot-spl.bin $(obj)u-boot.bin
-		$(MAKE) -C $(SRCTREE)/arch/arm/imx-common \
+		$(MAKE) $(build) $(SRCTREE)/arch/arm/imx-common \
 			$(OBJTREE)/u-boot-with-spl.imx
 
 $(obj)u-boot-with-nand-spl.imx: $(obj)spl/u-boot-spl.bin $(obj)u-boot.bin
-		$(MAKE) -C $(SRCTREE)/arch/arm/imx-common \
+		$(MAKE) $(build) $(SRCTREE)/arch/arm/imx-common \
 			$(OBJTREE)/u-boot-with-nand-spl.imx
 
 $(obj)u-boot.ubl:       $(obj)u-boot-with-spl.bin