usb: xhci: add missing dma-mapping.h includes

A randconfig build hit the following build errors because xhci.c and
xhci-mem.c use dma mapping functions but don't include
<linux/dma-mapping.h>. Add the missing includes to fix the build errors.

drivers/usb/host/xhci.c In function 'xhci_gen_setup':
drivers/usb/host/xhci.c +4872 : error: implicit declaration of function 'dma_set_mask'
drivers/usb/host/xhci.c +4872 : error: implicit declaration of function 'DMA_BIT_MASK'

drivers/usb/host/xhci-mem.c In function 'xhci_free_stream_ctx':
drivers/usb/host/xhci-mem.c +435 : error: implicit declaration of function 'dma_free_coherent'
drivers/usb/host/xhci-mem.c In function 'xhci_alloc_stream_ctx':
drivers/usb/host/xhci-mem.c +463 : error: implicit declaration of function 'dma_alloc_coherent'
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

drivers/usb/host/xhci-mem.c

@@ -24,6 +24,7 @@
 #include <linux/pci.h>
 #include <linux/slab.h>
 #include <linux/dmapool.h>
+#include <linux/dma-mapping.h>
 
 #include "xhci.h"
 

drivers/usb/host/xhci.c

@@ -27,6 +27,7 @@
 #include <linux/moduleparam.h>
 #include <linux/slab.h>
 #include <linux/dmi.h>
+#include <linux/dma-mapping.h>
 
 #include "xhci.h"