arm64: dts: rockchip: Add finer-grained PWM states for the fan on Rock 5C

Radxa Heatsink 6540B, which is the official cooling accessory for the
Rock 5C board, includes a small 5V fan, which in my testing spins up
reliably at a PWM setting of 24 (out of 255). It is also quite loud
at the current minimum setting of 64, and noticeably less so at 24.

Introduce two intermediate PWM states at the lower end of the fan's
operating range to enable better balance between noise and cooling.

Note further that, in my testing, having the fan run at 44 is enough
to keep the system from thermal throttling with sustained 100% load
on its 8 CPU cores (in 22C ambient temperature and no case)

Signed-off-by: Alexey Charkov <alchark@gmail.com>
Acked-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/20250120-rock-5c-fan-v1-1-5fb8446c981b@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

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