arm64: zynqmp: Do not assing MIO34 that early on zcu100

MIO34 is connected to POWER_KILL signal. When MIO configuration is done in
psu_init() and this pin is assigned to PMU but PMU configuration is not
loaded yet. PMU gpio output is high that means board is powered off
immediately.
The patch is fixing this sequence that MIO34 stays assing to ps gpio IP.
PMU config is loaded in SPL and then pin assigned to PMU through
psu_post_config_data().

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