powerpc/xive: Ensure active irqd when setting affinity

powerpc/xive: Ensure active irqd when setting affinity

Ensure irqd is active before attempting to set affinity. This should
make the set affinity code more robust. For instance, this prevents
these messages seen on a 4.12 based kernel when taking cpus offline:

   [  123.053037264,3] XIVE[ IC 00  ] ISN 2 lead to invalid IVE !
   [   77.885859] xive: Error -6 reconfiguring irq 17
   [   77.885862] IRQ17: set affinity failed(-6).

That particular case has been fixed in 4.13-rc1 by commit
4bb31a8d00b6 ("genirq/cpuhotplug: Do not migrated shutdown irqs").

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>