x86: vSMP: use pvops only if platform has the capability to support it

Re-arrange set_vsmp_pv_ops so that pv_ops are set only if
the platform has capability to support paravirtualized irq ops

Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>