Advertise the maximum offset the .adjphase callback is capable of
supporting in nanoseconds for IDT ClockMatrix devices. Depend on
ptp_clock_adjtime for handling out-of-range offsets. ptp_clock_adjtime
returns -ERANGE instead of clamping out-of-range offsets.

Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Vincent Cheng <vincent.cheng.xh@renesas.com>
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>