ptp: ptp_clockmatrix: Add adjphase() to support PHC write phase mode.

Add idtcm_adjphase() to support PHC write phase mode.

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