perf: Some perf-kvm documentation edits

asciidoc does not allow the "===" to be longer than the line
above it.
Also fix a couple types and formatting errors.

Signed-off-by: William Cohen <wcohen@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <4BD204C5.9000504@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>