arm64: zynqmp: Add support for new power-management node name

zynqmp-power node is going to be renamed to power-management which should
be generic enough. New name came from dt-binding review that's why there is
no way around. Add support new name but also at the same time check old
name just in case older dt binding is used.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/967aa76f9f72604c874b580476aa85f5260ccd65.1704448544.git.michal.simek@amd.com