AVR32: fix libusb build

The libc of the avr32 toolchains seem to lack the timerfd-associated
functions.

Pass --disable-timerfd to libusb configure script when building for
avr32.

Fixes most of the recent avr32 breakages, such as
http://autobuild.buildroot.org/results/f418b6c0b026891c27467f61444b6eac8c105681
or
http://autobuild.buildroot.org/results/1a9e571998bc0a40822dca84267abbdd969bab5e

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libusb/libusb.mk

@@ -11,5 +11,9 @@ LIBUSB_LICENSE_FILES = COPYING
 LIBUSB_DEPENDENCIES = host-pkgconf
 LIBUSB_INSTALL_STAGING = YES
 
+ifeq ($(BR2_avr32),y)
+LIBUSB_CONF_OPT += --disable-timerfd
+endif
+
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))