arm64: dts: rockchip: add rk356x sfc support

Add the sfc node to the rk356x device tree. This enables spi flash
support for this soc.

Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20220429115252.2360496-5-pgwipeout@gmail.com


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