dpll: zl3073x: make frequency monitor a per-device attribute

dpll: zl3073x: make frequency monitor a per-device attribute

The frequency monitoring feature uses shared hardware registers
that measure input reference frequencies independently of
individual DPLL channels. However, the freq_monitor flag was
incorrectly placed in the per-DPLL structure, causing each
channel to track its own enable/disable state independently.

Since the DPLL core calls measured_freq_get() only for the first
pin registration, the measured_freq_check() in the periodic worker
was gated by the per-DPLL freq_monitor flag of whichever channel
happens to be checked. If the first DPLL channel had frequency
monitoring disabled while another had it enabled, measurements
were never reported.

Move freq_monitor from struct zl3073x_dpll to struct zl3073x_dev
so all DPLL channels share a single flag, matching the hardware
behavior. Update freq_monitor_set() to notify other DPLL devices
about the change (like phase_offset_avg_factor_set() already does)
and remove the mode-dependent guard in zl3073x_dpll_changes_check()
since all input pin monitoring (pin state, phase offset, FFO, and
measured frequency) works correctly in all DPLL modes.

Fixes: bfc923b642874 ("dpll: zl3073x: implement frequency monitoring")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Link: https://patch.msgid.link/20260526074525.1451008-4-ivecera@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>