dpll: zl3073x: Add support to get fractional frequency offset

dpll: zl3073x: Add support to get fractional frequency offset

Adds support to get fractional frequency offset for input pins. Implement
the appropriate callback and function that periodicaly performs reference
frequency measurement and notifies DPLL core about changes.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Tested-by: Prathosh Satish <prathosh.satish@microchip.com>
Co-developed-by: Prathosh Satish <Prathosh.Satish@microchip.com>
Signed-off-by: Prathosh Satish <Prathosh.Satish@microchip.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Link: https://patch.msgid.link/20250715144633.149156-6-ivecera@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>