ptp: ocp: add serial port of mRO50 MAC on ART card

ART card provides interface to access to serial port of miniature atomic
clock found on the card. Add support for this device and configure it
during init phase.

Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Co-developed-by: Charles Parent <charles.parent@orolia2s.com>
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Vadim Fedorenko <vadfed@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>