AndroidKernel: Building dtb.img to support header version 2

The dtb.img is made by concatenating all the compiled dtbs
after the kernel is compiled. This dtb.img is then added to be
a part of the boot.img.

Change-Id: I7667d1c3118962bbc709a362a2b9a2b6419dede4
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>