device-fsl

MA-12523 build: boot image can not update automatically when make bootimage

Add kernel_imx source directory as kernel build dependency.

Change-Id: I61ea1ff6ecec41937e5c9499b7db4aee95eb6023
Signed-off-by: Jindong <jindong.yue@nxp.com>
Reviewed-on: http://androidsource.ap.freescale.net/project/5719
Reviewed-by: zhang sanshan <sanshan.zhang@nxp.com>