arm64: dts: rockchip: Add sdmmc_ext for RK3328

RK3328 SoC has a fourth mmc controller called SDMMC_EXT. Some
boards have sdio wifi connected to it. In order to use it
one would have to add the pinctrls from sdmmc0ext group which
is done on board level.

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Signed-off-by: Diederik de Haas <didi.debian@cknow.org>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/20240710132830.14710-3-didi.debian@cknow.org


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