pwm: argon-fan-hat: Add Argon40 Fan HAT support

Add trivial PWM driver for Argon40 Fan HAT, which is a RaspberryPi
blower fan hat which can be controlled over I2C. Model this device
as a PWM, so the pwm-fan can be attached to it and handle thermal
zones and RPM management in a generic manner.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Link: https://lore.kernel.org/r/20250629220757.936212-3-marek.vasut+renesas@mailbox.org


Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>