Add nios2 target to valid arch list definition.
Based on previous work by Walter Goossens <waltergoossens@home.nl>
at https://github.com/wgoossens/meta-nios2 .
(From OE-Core rev: f0af7d0d9316a6eeacc0686b8c4640491f255883)
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Walter Goossens <waltergoossens@home.nl>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>