lua-ev: disable on avr32 and blackfin

lua-ev is a reverse dependency of libev, but the architecture filtering is
not propagated. Fixes autobuild failure such as the following.

  http://autobuild.buildroot.net/results/387/38704a4362ab6c3458c45603975b274937059fa9/



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