arm64: versal: Add support to load an app at EL1

Add support to switch to EL1 and load an EL1 app from U-Boot which is
executing at EL2 or EL3 in aarch64 mode.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Link: https://lore.kernel.org/r/20220506055345.1921-1-ashok.reddy.soma@xilinx.com


Signed-off-by: Michal Simek <michal.simek@amd.com>