arm64: dts: rockchip: add rk3588 spi aliases to soc dtsi

The spi controllers on rk3588 are named spi0 - spi4. Board schematics
also use these exact numbers and we want those names to also reflect
in the OS devices because everything else would just cause confusion.
Userspace spi access is a thing afterall.

To prevent each board repeating their list of spi aliases, define them
in the soc dtsi, as previous Rockchip soc like the rk356x do already.

Signed-off-by: Heiko Stuebner <heiko.stuebner@cherry.de>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/20231205164842.556684-5-heiko@sntech.de