powerpc/numa: Use ibm,architecture-vec-5 to detect form 1 affinity

I've been told that the architected way to determine we are in form 1
affinity mode is by reading the ibm,architecture-vec-5 property which
mirrors the layout of the fifth vector of the ibm,client-architecture
structure.

Eventually we may want to parse the ibm,architecture-vec-5 and create
FW_FEATURE_* bits.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>