Make the microblaze toolchains easily distinguishable

It was confusing to have two different toolchains with the
same label.

Signed-off-by: Jan Viktorin <xvikto03@stud.fit.vutbr.cz>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>