ptp: ocp: Update devlink firmware display path.

Cache the firmware version when the card is initialized,
and use this field to populate the devlink firmware information.

The cached firmware version will be used for feature gating in
upcoming patches.

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