configs: versal: update initial stack pointer

configs: versal: update initial stack pointer

The mini u-boot is hanging because of an initial stack
pointer address is used at half of the memory, when mini
u-boot is called reloc_fdt() function and doing memcpy()
for the fdt before relocation, and there is no sufficient
memory for the stack pointer. To fix, set an initial stack
pointer address to near the top of memory. The new stack
pointer address is assigned before calling the relocate
of u-boot based on the stack relocate calculation and
this new stack pointer is used while executing u-boot
from the relocated memory.

Signed-off-by: Padmarao Begari <padmarao.begari@amd.com>
Link: https://lore.kernel.org/r/20250203090409.844403-1-padmarao.begari@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>