usb: add HAS_IOMEM dependency to USB_XHCI_MVEBU

drivers/usb/host/xhci-mvebu.c: In function ‘xhci_mvebu_mbus_init_quirk’:
drivers/usb/host/xhci-mvebu.c:58:2: error: implicit declaration of function ‘ioremap’ [-Werror=implicit-function-declaration]
  base = ioremap(res->start, resource_size(res));
  ^
drivers/usb/host/xhci-mvebu.c:58:7: warning: assignment makes pointer from integer without a cast [enabled by default]
  base = ioremap(res->start, resource_size(res));
       ^
drivers/usb/host/xhci-mvebu.c:69:2: error: implicit declaration of function ‘iounmap’ [-Werror=implicit-function-declaration]
  iounmap(base);
  ^

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>