Use the change of NR to detect whether an asynchronous branch is a VM-Exit.

Note VM-Entry is determined from the vmlaunch or vmresume instruction,
in which case, sample flags will show "VMentry" even if the VM-Entry fails.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210218095801.19576-10-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>