ptp: ocp: Add the mapping for the external PPS registers.

There are two PPS blocks: one handles the external PPS signal output,
with the other handling the PPS signal input to the internal clock.
Add controls for the external PPS block.

Rename the fields so they match their function.

Add cable_delay to the register definitions.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>