firmware: zynqmp: Move loading message to debug

Power domain driver is using this function for every IP which is PD listed.
This can end up with a lot of messages which end up in boot log. That's why
show it only in EL3 as was used in past.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/d73fc8bc663110b6e8d5e70fdb6435d1199e9db8.1642163135.git.michal.simek@xilinx.com