This implements hid_if.m methods for HID-over-USB protocol .
Also, this adds USBHID_ENABLED kernel option which changes device_probe()
priority and adds/removes PnP records to prefer usbhid over ums, ukbd, wmt
and other USB HID device drivers.
The module is based on uhid(4) driver.
It is disabled by default for now due to conflicts with existing USB HID drivers.