arm64: dts: rockchip: Enable SD card detection for Rock960 boards

For proper working of SD cards, let's add the Card Detect GPIO property
to the common devicetree for Rock960 family boards.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>