ARM: dts: rockchip: Add the SDIO wifi on Radxa Rock2 square

Enable the sdio0 slot on the Rock2 square which has a broadcom wifi chip
attached and add a power sequence to enable the wifi chip and turn on
the required 32k clock.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>