Handle parameters similar to dbgp=ehci.
Implement this by not resettting dbc->sbdf again in dbc_init_xhc(), but
using a value found there if non-zero. Additionally, add xue->xhc_num to
select n-th controller.
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>