leds: leds-is31fl32xx: Add support for is31fl3236a

Also add an additional and optional control register for setting the
output PWM frequency to 22kHz. The default is 3kHz and this option puts
the operational frequency outside of the audible range.

Signed-off-by: Pawel Zalewski <pzalewski@thegoodpenguin.co.uk>
Link: https://lore.kernel.org/r/20250723-leds-is31fl3236a-v6-3-210328058625@thegoodpenguin.co.uk


Signed-off-by: Lee Jones <lee@kernel.org>