Add new functions to return some of the get_srcrev data in new and different
ways. We need two different forms of the data, one is a string to inject into
PKGV, the other is the full revisions as a string to include in hash computations
so that the hash changes when the input revisions change.
This allows us to clean up and simplify the code in OE-Core and move the
version information from PV to PKGV.
(Bitbake rev: ae4dfa2a31c74c0c6c2b14cece822ed1f3d79723)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>