device-fsl

MA-15722-5 make dtbo image depend on dtb files instead of dts files

when modifications are made on the files included by the dts file to be
compiled to dtb file, the status of dtbo image file generated last time
and the dts file both keep unchanged, the dts file is no newer than the
dtbo image, dtbo image will not be updated.

make the dtbo image target depend on the dtb files instead of dts files,
changes made on dts file and other files included by this dts file will
update the dtb file, then dtb file is newer than dtbo image, then dtbo
image will be updated.

Change-Id: I9356d96e9e39510c637a9f839c8089ff7bf48e63
Signed-off-by: faqiang.zhu <faqiang.zhu@nxp.com>
Reviewed-on: http://androidsource.ap.freescale.net/project/11083
Reviewed-by: guoyin.chen <guoyin.chen@nxp.com>