net: pcs: xpcs: export xpcs_probe

Similar to the other recently functions, it is not necessary for
xpcs_probe to be a function pointer, so export it so that it can be
called directly.

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