bigos: add early prototype for PEBS

Add various, messy stuff for PEBS integration into Xen.
Need a lot of refactoring, but all the basic blocks are here.
bigos: add a lot of messy stuff for PEBS

Add a lot of mess for set up a decent API for PEBS.
bigos: add a clean PEBS API

The big PEBS mess is becoming a nice and usable API.
Still need to remove useless stuff.
bigos: add a stable version on PEBS monitoring

Move the PEBS API in asm/pebs.
Add a generic monitoring interface in xen/monitor which currently
only calls the PEBS monitoring functions.
This last monitoring interface is used in the version hypercall.
Merge branch 'pebs' into develop