arm64: dts: allwinner: sun50i: a64: Add spi flash node for sopine

The Sopine and Pine64-LTS have a winbond w25q128 spi flash on spi0.
Add a node for it.

Signed-off-by: Emmanuel Vadot <manu@freebsd.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>