KVM: x86 emulator: fix RDPMC privilege check

RDPMC is only privileged if CR4.PCE=0.  check_rdpmc() already implements this,
so all we need to do is drop the Priv flag.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>