USB: make urb scatter-gather support more generic

The WHCI HCD will also support urbs with scatter-gather lists.  Add a
usb_bus field to indicated how many sg list elements are supported by
the HCD.  Use this to decide whether to pass the scatter-list to the HCD
or not.

Make the usb-storage driver use this new field.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/xhci-pci.c

@@ -54,6 +54,8 @@ static int xhci_pci_setup(struct usb_hcd *hcd)
 	struct pci_dev		*pdev = to_pci_dev(hcd->self.controller);
 	int			retval;
 
+	hcd->self.sg_tablesize = TRBS_PER_SEGMENT - 1;
+
 	xhci->cap_regs = hcd->regs;
 	xhci->op_regs = hcd->regs +
 		HC_LENGTH(xhci_readl(xhci, &xhci->cap_regs->hc_capbase));