arm64: zynqmp: Add support for zynqmp nvmem firmware driver

Add support for zynqmp nvmem firmware driver.

Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
[m.tretter@pengutronix.de: move to subnode of firmware]
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>