arm64: dts: rockchip: Add pwm-fan to rk3588-rock-5b

Add the necessary DT changes for the Rock 5B board to enable support for
the PWM controlled heat sink fan.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Reviewed-by: Christopher Obbard <chris.obbard@collabora.com>
Link: https://lore.kernel.org/r/20230404173807.490520-3-cristian.ciocaltea@collabora.com


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