arm64: dts: rockchip: enable UART5 on RK3588 Tiger Haikou

arm64: dts: rockchip: enable UART5 on RK3588 Tiger Haikou

In its default configuration (SW2 on "UART1"), UART5 is exposed on the
DB9 RS232/RS485 connector. While the same signals are also exposed on
Q7_GPIO5 and Q7_GPIO6, a GPIO header, and thus could be used for other
purposes, RK3399 Puma Haikou and PX30 Ringneck Haikou do enable the UART
controller exposed on the DB9 connector, so let's keep consistency
across our modules and enable it on RK3588 Tiger Haikou by default too.

Add a comment while at it to explicit where this controller is routed
to.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Link: https://lore.kernel.org/r/20250218-tsd-align-haikou-v1-1-5c44d1dd8658@cherry.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>