arm64: zynqmp: Add device tree properties for nand flash

Add ecc strength & ecc step size properties for nand flash devices,
when operating in software-ecc mode.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/866f4b888129ff0213df9cdb51b5529b199fb7b7.1631713594.git.michal.simek@xilinx.com