meta-cedartrail merges yocto/pvr via the back-end kernel tooling, but
there's nothing to tell it when it needs to be re-fetched.

Add pvr to the SRC_URI along with its current SRCREV, so the git
fetcher can determine whether or not it needs to refetch the repo.

Fixes [YOCTO #2294].

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>