device-fsl

MA-15077 build: uboot can't update unless touch obj/UBOOT_OBJ

$(UBOOT_BIN) depends on $(UBOOT_OUT), so need touch
obj/UBOOT_OBJ, then uboot can be built again.

$(UBOOT_BIN) is u-boot.imx, which is not used.
Now remove $(UBOOT_BIN) after uboot built finished,
to make uboot can always be built.

Change-Id: I60856290404e387f2566a0a7159b4779af2e5c66
Signed-off-by: Jindong <jindong.yue@nxp.com>
Reviewed-on: http://androidsource.ap.freescale.net/project/9081
Reviewed-by: zhang sanshan <sanshan.zhang@nxp.com>
Reviewed-on: http://androidsource.ap.freescale.net/project/9324