usbdevfs: Use scatter-gather lists for large bulk transfers

usbdevfs: Use scatter-gather lists for large bulk transfers

When using urb->transfer_buffer we need to allocate physical contiguous buffers
for the entire transfer, which is pretty much guaranteed to fail with large
transfers.

Currently userspace works around this by breaking large transfers into multiple
urbs. For large bulk transfers this leads to all kind of complications.

This patch makes it possible for userspace to reliable submit large bulk
transfers to scatter-gather capable host controllers in one go, by using a
scatterlist to break the transfer up in managable chunks.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>