toolchain-external: bump CodeSourcery NIOSII to 2015.11

Some package black list CS NIOSII toolchains, mainly due to _gp link
issue. A follow up patch can remove the restriction case by case.

Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Reviewed-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Tested-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>