trousers: disable on ARC

This package has been failing to build on ARC due to a toolchain bug
since December 2015, causing a total of 168 build failures. Therefore,
let's disable this package for now, until the toolchain issue gets
resolved.

Fixes^Wavoids:

  http://autobuild.buildroot.net/results/e65d1d7c5a4dd4616167cfe2aa938be6af139602/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>