PMU virtualization needs to talk to Intel-specific bits of perf; these are
only available when CPU_SUP_INTEL=y.

Fixes

  arch/x86/built-in.o: In function `atomic_switch_perf_msrs':
  vmx.c:(.text+0x6b1d4): undefined reference to `perf_guest_get_msrs'
Reported-by: NIngo Molnar <mingo@elte.hu>
Reported-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>