arm64: zynqmp: Do not include psu_init to U-Boot by default

The commit ed35de61 ("Convert CONFIG_ZYNQMP_PSU_INIT_ENABLED to
Kconfig") converted CONFIG_ZYNQMP_PSU_INIT_ENABLED symbol and enabled it by
default which is not correct configuration.
Intention of this config was to have it enabled by default for SPL and
provide an option to users to also do low level initialization directly
from U-Boot.
That's why it is necessary to define second symbol with SPL marking in it
and properly use symbols depends on usage in Makefile.
Also disable ZYNQMP_PSU_INIT_ENABLED from boards which enables it by
default. CONFIG_SPL_ZYNQMP_PSU_INIT_ENABLED is enabled by default when SPL
is enabled.

Reported-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/d5fcbd66b05bf0d7ef594e66464ee23b48c5e4cc.1669969083.git.michal.simek@amd.com