net: dsa: felix: move the PTP clock structure to felix_vsc9959.c

Not only does Sevile not have a PTP clock, but with separate modules,
this structure cannot even live in felix.c, due to the .owner =
THIS_MODULE assignment causing this link time error:

drivers/net/dsa/ocelot/felix.o:(.data+0x0): undefined reference to `__this_module'

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>