powerpc/xics: Initialization code cleanups

We only need to check the ibm,interrupt-server#-size property once, not
once per global server and thread.

We can use !CONFIG_SMP cpu masks and hard_smp_processor_id() to avoid an ifdef.
Put the node when breaking out of the loop on lpar systems.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>