arm64: versal: Add mini configuration for Versal

This patch adds new mini target for versal.
This configuration is very minimal in size which runs
from OCM. It contains support for mtest which can be
used for running DDR memory tests.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>