xilinx: use get_mem_top() to compute ram_top

xilinx: use get_mem_top() to compute ram_top

Use the get_mem_top function to compute the value of ram_top. This was
earlier done through LMB API's, which are no longer available till
after relocation. Use get_mem_top() instead to compute the ram_top
value.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Tested-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20241025172724.195093-3-sughosh.ganu@linaro.org
Signed-off-by: Michal Simek <michal.simek@amd.com>