arm64: dts: rockchip: Enable MTD Flash on rk3399-roc-pc

rk3399-roc-pc has 16 MB SPI NOR Flash, enable it.

Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Link: https://lore.kernel.org/r/94f44e1d-86c6-1e32-aa63-56edbd7d75f5@fivetechno.de


Signed-off-by: Heiko Stuebner <heiko@sntech.de>