arm64: dts: sparx5: Add spi-nand devices

This patch add spi-nand DT nodes to the applicable Sparx5 boards.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Link: https://lore.kernel.org/r/20200824203010.2033-7-lars.povlsen@microchip.com