toolchain-external: Version bump to 2013.05 release for MIPS

Remove old 2011.09 release. Allow MIPS64 cores on
2013.05 release since they are supported by the toolchain.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>