usb: Convert usb_packet_{map, unmap} to universal DMA helpers

The USB UHCI and EHCI drivers were converted some time ago to use the
pci_dma_*() helper functions.  However, this conversion was not complete
because in some places both these drivers do DMA via the usb_packet_map()
function in usb-libhw.c.  That function directly used
cpu_physical_memory_map().

Now that the sglist code uses DMA wrappers properly, we can convert the
functions in usb-libhw.c, thus conpleting the conversion of UHCI and EHCI
to use the DMA wrappers.

Note that usb_packet_map() invokes dma_memory_map() with a NULL invalidate
callback function.  When IOMMU support is added, this will mean that
usb_packet_map() and the corresponding usb_packet_unmap() must be called in
close proximity without dropping the qemu device lock - otherwise the guest
might invalidate IOMMU mappings while they are still in use by the device
code.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/usb/hcd-uhci.c

@@ -871,7 +871,7 @@ static int uhci_handle_td(UHCIState *s, uint32_t addr, UHCI_TD *td,
 
 done:
     len = uhci_complete_td(s, td, async, int_mask);
-    usb_packet_unmap(&async->packet);
+    usb_packet_unmap(&async->packet, &async->sgl);
     uhci_async_free(async);
     return len;
 }