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>
Change-Id: If9a9ff9edde614ce8a87aec1471bd7b702f78808
Git-commit: 008eb957dafea32bac993be5cbeaf4ca0ee8b0aa
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Jack Pham <jackp@codeaurora.org>