net: dsa: ocelot: define PTP registers for felix_vsc9959

This patch is to define PTP registers for felix_vsc9959.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>