xilinx: firmware: Introduce zynqmp_pmufw_node() for loading PMU fragments

Introduce zynqmp_pmufw_node() for loading PMU configuration fragment for
enabling IPs. Firmware driver has small overlay where NODE id is added and
config fragment is sent to PMUFW. There is a need to build PMUFW with
fragment support.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/636e8150bd4e2b1f988d59795772c685ceeec083.1642163135.git.michal.simek@xilinx.com