x86: KVM geust: make setup_secondary_clock definition dependent on local apic

Since the pv_apic_ops are only present if CONFIG_X86_LOCAL_APIC is compiled
in, kvmclock failed to build without this option.  This patch fixes this.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>