dpll: zl3073x: Allow to configure phase offset averaging factor

dpll: zl3073x: Allow to configure phase offset averaging factor

The DPLL phase measurement block uses an exponential moving average with
a configurable averaging factor. Measurements are taken at approximately
40 Hz or at the reference frequency, whichever is lower.

Currently, factor=2 is used to prioritize fast response for dynamic
phase changes. For applications needing a stable, precise average phase
offset where rapid changes are unlikely, a higher factor is recommended.

Implement the .phase_offset_avg_factor_get/set callbacks to allow a user
to adjust this factor.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20250927084912.2343597-4-ivecera@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>