bitbake: fetch2: Avoid using FILESDIR in unpack

bitbake: fetch2: Avoid using FILESDIR in unpack

Currently there is code which uses FILESDIR in unpack to ensure
parent directories are created, leading to differing behaviour depending on
which search path is used to locate the directory.

This change standardises the code and takes the data from the fetcher in
question meaning we can standardise the code and deprecate FILESDIR.

(Bitbake rev: 1cccb3bd01ed82e4978acfef0fda1bd797eef72a)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>