net: mscc: ocelot: move ocelot ptp clock code out of ocelot.c

The Ocelot PTP clock driver had been embedded into ocelot.c driver.
It had supported basic gettime64/settime64/adjtime/adjfine functions
by now which were used by both Ocelot switch and Felix switch.

This patch is to move current ptp clock code out of ocelot.c driver
maintaining as a single ocelot_ptp.c.
For futher new features implementation, the common code could be put
in ocelot_ptp.c and the switch specific code should be in specific
switch driver. The interrupt implementation in SoC is different
between Ocelot and Felix.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>