dpll: zl3073x: Cache reference monitor status

dpll: zl3073x: Cache reference monitor status

Instead of reading the ZL_REG_REF_MON_STATUS register every time
the reference status is needed, cache this value in the zl3073x_ref
struct.

This is achieved by:
* Adding a mon_status field to struct zl3073x_ref
* Introducing zl3073x_dev_ref_status_update() to read the status for
  all references into this new cache field
* Calling this update function from the periodic work handler
* Adding zl3073x_ref_is_status_ok() and zl3073x_dev_ref_is_status_ok()
  helpers to check the cached value
* Refactoring all callers in dpll.c to use the new
  zl3073x_dev_ref_is_status_ok() helper, removing direct register reads

This change consolidates all status register reads into a single periodic
function and reduces I/O bus traffic in dpll callbacks.

Reviewed-by: Petr Oros <poros@redhat.com>
Tested-by: Prathosh Satish <Prathosh.Satish@microchip.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Link: https://patch.msgid.link/20251113074105.141379-4-ivecera@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>