hw/arm/boot: pass an address limit to and return size from load_dtb()

Add an address limit input parameter to load_dtb() so that we can
tell load_dtb() how much memory the dtb is allowed to consume. If
the dtb doesn't fit, return 0, otherwise return the actual size of
the loaded dtb.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Message-id: 1410453915-9344-3-git-send-email-ard.biesheuvel@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
