usb: add HAS_IOMEM dependency to USB_EHCI_HCD

usb: add HAS_IOMEM dependency to USB_EHCI_HCD

drivers/built-in.o: In function `ehci_platform_probe':
/home/vegard/linux/drivers/usb/host/ehci-platform.c:282: undefined reference to `devm_ioremap_resource'
drivers/built-in.o: In function `oxu_drv_probe':
/home/vegard/linux/drivers/usb/host/oxu210hp-hcd.c:3821: undefined reference to `devm_ioremap_resource'
drivers/built-in.o: In function `isp1362_probe':
/home/vegard/linux/drivers/usb/host/isp1362-hcd.c:2668: undefined reference to `devm_ioremap_resource'

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>