drivers/usb: Move conditional compilation to Makefile

drivers/usb/Makefile

drivers/usb/isp116x-hcd.c

drivers/usb/sl811_usb.c

drivers/usb/usb_ohci.c

drivers/usb/usbdcore_ep0.c

drivers/usb/usbdcore_mpc8xx.c

drivers/usb/usbdcore_omap1510.c