arm64: versal: Add new jtag distro boot command

This patch adds new jtag distro boot command to look for bootscript file
in DDR and execute it first incase of jtag bootmode.
This patch also updates scriptaddr to 512MB as there is high of script
corruption incase of bigger kernel image.

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