libpayload: reintroduce optional PCI in XHCI driver

being a good citizen on the box, libpayload tries to return to EHCI
mode on shutdown, so a non-XHCI capable USB driver after it (eg. in
the OS) finds something to work with.

Change-Id: Id227d646e08a258b841c644263112f0815dd486c
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/4547
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
3 files changed