fix(plat/marvell/a8k): Require that MV_DDR_PATH is correctly set

Target mrvl_flash depends on external mv_ddr source code which is not
part of TF-A project. Do not expect that it is pre-downloaded at some
specific location and require user to specify correct path to mv_ddr
source code via MV_DDR_PATH build option.

TF-A code for Armada 37x0 platform also depends on mv_ddr source code
and already requires passing correct MV_DDR_PATH build option.

So for A8K implement same checks for validity of MV_DDR_PATH option as
are already used by TF-A code for Armada 37x0 platform.

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I792f2bfeab0cec89b1b64e88d7b2c456e22de43a
2 files changed