ptp: Add a ptp clock driver for IDT ClockMatrix.

The IDT ClockMatrix (TM) family includes integrated devices that provide
eight PLL channels.  Each PLL channel can be independently configured as a
frequency synthesizer, jitter attenuator, digitally controlled
oscillator (DCO), or a digital phase lock loop (DPLL).  Typically
these devices are used as timing references and clock sources for PTP
applications.  This patch adds support for the device.

Co-developed-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Vincent Cheng <vincent.cheng.xh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>