xenomai: enable armv5tej support

The br-arm-full-2013.11-rc2 toolchain is builded with arch=armv5te
and tune=arm926ej-s, which is not recognized by xenomai.

fixes: http://autobuild.buildroot.net/results/e3b/e3b534dafb6dd7d788b0c3629ccc0b25702790f0/build-end.log

This patch has already been merged upstream:

http://git.xenomai.org/xenomai-2.6.git/commit/?id=ebc2779baa222db4a5936c3d3022803355585b8c



Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>