libhid: disable on avr32

libhid uses timerfd, which is not yet available in the uClibc-0.9.31
that we have to rely on for avr32.  Since this is pretty much a corner
case, just disable libhid for avr32.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>