arm64: dts: rockchip: Add UART9 (bluetooth) to Khadas Edge 2

Khadas Edge 2 has onboard AP6275P Wi-Fi6 (PCIe2) and BT5 (UART9) module.
This commit enables UART9.

Signed-off-by: Muhammed Efe Cetin <efectn@protonmail.com>
Link: https://lore.kernel.org/r/0a10afeff3aec3a8bccca2dbe4e65f7b4a2c4666.1708381247.git.efectn@protonmail.com


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