xenomai: bump to version 2.6.2.1

- remove BR2_PACKAGE_XENOMAI_SMP since xenomai 2.6.2 no more
requires to pass the --enable-smp option : see release notes at
http://www.xenomai.org/index.php/Xenomai:News#2012-12-26_Xenomai_2.6.2



- remove xenomai-thumb-fix.patch since it was completely merged
in xenomai 2.6.2

Signed-off-by: Victor Hiairrassary <victor.hiairrassary.ml@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>