We need a separate fetcher cache per multiconfig as the revisions and other
SRC_URI data can potentially be different. For now, this is the simplest way
to achieve that and avoids linux-yocto kernel build failures when targeting
multiple machines for example.
(Bitbake rev: d98cc31d6668bc1d6372664593126b5e5132ef2c)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>