repo: Use separate task for patching repo rev

Using a task instead of a version specific patch for setting the repo
revision within the source code. This drastically decreases the
maintenance burden and easier usage of the OE update helper.

Signed-off-by: Jasper Orschulko <Jasper.Orschulko@iris-sensing.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>