arm64: dts: rockchip: Add dtsi entry for RK3399 PCIe endpoint core

arm64: dts: rockchip: Add dtsi entry for RK3399 PCIe endpoint core

Add dtsi entry for RK3399 PCIe endpoint core in the device tree.
The status is "disabled" by default, so it will not be loaded unless
explicitly chosen to. The RK3399 PCIe endpoit core should be enabled
with the RK3399 PCIe root complex disabled because the RK3399 PCIe
controller can only work one mode at the time, either in "root complex"
mode or in "endpoint" mode.

Tested-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Rick Wertenbroek <rick.wertenbroek@gmail.com>
Link: https://lore.kernel.org/r/20230418074700.1083505-6-rick.wertenbroek@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>