Allow sched domain setup to be overridden by arch code. This functionality
is needed again.

From: Paul Jackson <pj@sgi.com>

  Builds of 2.6.9-rc1-mm5 ia64 NUMA configs fail, with many complaints that
  SD_NODE_INIT is defined twice, in asm/processor.h and linux/sched.h.

  I guess that the preprocessor conditionals were wrong when Nick added the
  per-arch override ability again of SD_NODE_INIT were wrong.  At least this
  change lets me rebuild ia64 again.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>