arm64: dts: rockchip: Lower SD card speed on rk3399 Pinebook Pro

MicroSD card slot in the Pinebook Pro is located on a separate
daughterboard that's connected to the mainboard using a rather
long flat cable.  The resulting signal degradation causes many
perfectly fine microSD cards not to work in the Pinebook Pro,
which is a common source of frustration among the owners.

Changing the mode and lowering the speed reportedly fixes this
issue and makes many microSD cards work as expected.

Co-developed-by: Dragan Simic <dragan.simic@gmail.com>
Signed-off-by: Dragan Simic <dragan.simic@gmail.com>
Tested-by: JR Gonzalez <jrg@scientiam.org>
Signed-off-by: Dan Johansen <strit@manjaro.org>
Link: https://lore.kernel.org/r/20230305104730.15849-1-strit@manjaro.org


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