pkgv: Fix versioning
The gitpkgv.bbclass states:
gitpkgv.bbclass assumes the git repository has been cloned, and
contains SRCREV. So ${GITPKGV} and ${GITPKGVTAG} should never be
used in PV, only in PKGV. It can handle SRCREV = ${AUTOREV}, as
well as SRCREV = "<some fixed git hash>".
Change the version variables from PV to PKGV.