bitbake/fetch2: Fix the problems introduced by the git fetcher AUTOREV fix

bitbake/fetch2: Fix the problems introduced by the git fetcher AUTOREV fix

The ordering constrains on the urldata_init functions are not straight
forward. To avoid further problems, create a helper function to setup
the source revisions which the init functions can all at the appropriate
point.

(From Poky rev: c4371138f7444ecaa1fdd2b1ee4949fbc819f886)

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