xilinx: versal-net: Fix SYS_LOAD_ADDR to point to OCM

Versal NET mini U-Boot configuration is used for memory testing that's why
load address can't be really placed in memory which doesn't need to work
that's why move it to start of OCM which is the same memory which U-Boot is
running from.

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