arm64: zynqmp: Rename zynqmp-power node to power-management

Rename zynqmp-power node name to power-management which is more aligned
with generic node name recommendation.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/a2f7fe30e3630c262c2773a595b7a0c8918573a0.1704359569.git.michal.simek@amd.com