arm64: dts: rockchip: Add NanoPC T6

Add the NanoPC T6, a single board computer from FriendlyElec based on
the RK3588.

Initial device tree supports debug UART, SD, eMMC, PCIe 3, PMIC,
and 40 pin GPIO assignments.

Signed-off-by: Thomas McKahan <tmckahan@singleboardsolutions.com>
Link: https://lore.kernel.org/r/20230809112120.99-3-tmckahan@singleboardsolutions.com


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