hw/arm/boot: enable DTB support when booting ELF images

Add support for loading DTB images when booting ELF images using
-kernel. If there are no conflicts with the placement of the ELF
segments, the DTB image is loaded at the base of RAM.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Message-id: 1410453915-9344-5-git-send-email-ard.biesheuvel@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>