base/package: Move source revision information from PV to PKGV

base/package: Move source revision information from PV to PKGV

Source control information being present in PV used to be a hard requirement
for bitbake to operate correctly. Now that hashes are a required part of task
stamps, this requirement no longer exists.

This means we can defer the hash pieces to PKGV and simplify PV.

Use new bitbake fetcher API to inject the source revisions directly into the hash
allowing removal of some horrible code from base.bbclass and avoiding any hardcoding
about how SRCREV may or may not be used.

Use that API to object the string to append to PKGV and append that directly.

The user visible effect of this change is that PV will no longer have revision
information in it and this will now be appended to PV through PKGV when the
packages are written. Since PV is used in STAMP and WORKDIR, users will see
small directory naming and stamp naming changes.

This will mean that sstate reuse through hash equivalence where the source
revision changes but the output does not will become possible as the sstate
naming will become less specific and no longer contain the revision.

The SRCPV variable will no longer be needed in PV and is effectively now just
a null operation. Usage can be removed over time.

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