hwmon: (lm63) expose PWM frequency and LUT hysteresis as writable

The driver caches the PWM frequency register and the CONFIG_FAN slow-clock
select bit, but never lets userspace pick a different output frequency.
Add a pwm1_freq sysfs attribute that selects the closest SCS + PFR
combination for the requested value in Hz, gated by manual mode like
set_pwm1(). PFR is clamped to 31 so that 2*PFR fits in the chip's 6-bit
PWM register (matching the existing scaling assumption in show_pwm1).

The hardware LUT hysteresis register is shared by all LUT entries, so
the per-point pwm1_auto_pointN_temp_hyst attributes can't be made RW
without N-to-1 cross-attribute side effects. Following the max31760
precedent, expose a single chip-wide pwm1_auto_point_temp_hyst attribute
holding the hysteresis amount in millidegrees; the per-point attributes
stay RO and continue to show the resulting absolute trip-down
temperature for each entry.

This was tested on a Linksys LGS328MPC switch hardware where the fan
would not spin with the default PWM Frequency, which is why this change
is required.

Signed-off-by: Jan-Henrik Bruhn <kernel@jhbruhn.de>
Link: https://lore.kernel.org/r/20260523133617.3439102-1-kernel@jhbruhn.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

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