tracing/x86: Don't use mcount in kvmclock.c

The guest can use the paravirt clock in kvmclock.c which is used
by sched_clock(), which in turn is used by the tracing mechanism
for timestamps, which leads to infinite recursion.

Disable mcount/tracing for kvmclock.o.

Cc: stable@kernel.org
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>