arm64: versal: Define board_late_init for versal

arm64: versal: Define board_late_init for versal

Define board_late_init which performs bootmode detection
and prepares corresponding distro boot commaand sequence.

Also disable it for mini platforms because simply there is no need to have
it enabled.
But also disable it for virtual platform because Qemu is not modelling this
register space that's why travis testing would fail. This configuration
should be reverted when mainline Qemu is updated.

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