x86: rate-limit logging in do_xen{oprof,pmu}_op()

x86: rate-limit logging in do_xen{oprof,pmu}_op()

Some of the sub-ops are acessible to all guests, and hence should be
rate-limited. In the xenoprof case, just like for XSA-146, include them
only in debug builds. Since the vPMU code is rather new, allow them to
be always present, but downgrade them to (rate limited) guest messages.

This is CVE-2015-7971 / XSA-152.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Ian Campbell <ian.campbell@citrix.com>