Update following new Gnttab, Eventchn interface changes
Add the code to register the mirage Blkif
Add the blkfront interface from mirage-platform
Update to match the modified ring signature.
Add an explicit 'register' function to register the Device provider
Add a resume hook.
Merge pull request #1 from djs55/sync-eventchn-with-xen

Move to out-of-tree blkfront