dpll: zl3073x: Add support to get phase offset on connected input pin

dpll: zl3073x: Add support to get phase offset on connected input pin

Add support to get phase offset for the connected input pin. Implement
the appropriate callback and function that performs DPLL to connected
reference phase error measurement and notifies DPLL core about changes.

The measurement is performed internally by device on background 40 times
per second but the measured value is read each second and compared with
previous value.

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/20250715144633.149156-3-ivecera@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>