thunderbolt: Add functions for enabling and disabling lane bonding on XDomain

These can be used by service drivers to enable and disable lane bonding
as needed.

Signed-off-by: Isaac Hazan <isaac.hazan@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Yehezkel Bernat <YehezkelShB@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>