power: zynqmp: Use zynqmp_pmufw_node() from firmware

Remove private xpm_configobject[] and use zynqmp_pmufw_node() which
provides the same functionality.
Also add debug messages for easier debugging.

Fixes: e0283cbd ("power: zynqmp: Add power domain driver for ZynqMP")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Link: https://lore.kernel.org/r/bddf11459b9b9e849fac9a50db2f1a5fdfae4119.1646122254.git.michal.simek@xilinx.com