arm64: dts: allwinner: a64: Orange Pi Win: Add SPI flash node

The Orange Pi Win comes with 2 MB SPI flash, add the node.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>