ARM: dts: suniv: licheepi-nano: add SPI flash

Most LicheePi Nano boards come with soldered SPI flash, so enable SPI0
in the .dts and describe the flash chip. There is evidence of different
flash chips used, also of boards with no flash chip soldered, but the
Winbond 16MiB model is the most common, so use that for the compatible
string.  The actual flash chip model will be auto-detected at runtime
anyway.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220317162349.739636-13-andre.przywara@arm.com