hafnium: add device tree compiler

Hafnium's build requires the device tree compiler tool.
Until now the dtc binary was provided by the project's prebuilts
submodule. Moving forward prefer sourcing the tool from the docker
image.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: Ib740efbb32f21b92c4c882033bb2d0fa4f4358ad
1 file changed