libevas: disable on avr32

Neither epoll_create1 nor inotify_init1 is available on avr32. Fixes build
failures such as the following.

  http://autobuild.buildroot.net/results/4d435a5fc608936362d605aca696c01023be9723



Signed-off-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>