kernel/linux: add alternate download locations

Some longterm versions are not in the usual directory.
Account for these new locations.

Get rid of the mirror location, now that the main kernel site is
(almost) back to normal operations.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Blackfin specific configuration file

## select ARCH_SUPPORTS_32

## select ARCH_DEFAULT_32

## select ARCH_DEFAULT_LE

## select ARCH_SUPPORTS_WITH_ARCH

## select ARCH_SUPPORTS_WITH_CPU

## select ARCH_SUPPORTS_WITH_TUNE

## select ARCH_SUPPORTS_WITH_FPU

##

## help The Blackfin architecture