toolchain-external: bump Linaro ARM toolchains to 2013.04 and 2013.05

We add support for Linaro 2013.04 and Linaro 2013.05 and remove
support for Linaro 2013.01 and Linaro 2013.02.

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