powerpc: Reformat SD_NODE_INIT to match x86

Clean up SD_NODE_INITS so we can easily compare it to x86. Similar to the
work in 47734f89 (sched: Clean up topology.h)

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