thunderbolt: Move tb_switch_phy_port_from_link() to thunderbolt.h

A Thunderbolt service might need to find the physical port from a link
the cable is connected to. For instance networking driver uses this
information to generate MAC address according the Apple ThunderboltIP
protocol.

Move this function to thunderbolt.h and rename it to
tb_phy_port_from_link() to reflect the fact that it does not take switch
as parameter.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Michael Jamet <michael.jamet@intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>