powerpc/mm: Add SAO Feature bit to the cputable

Add the CPU feature bit for the new Strong Access Ordering
facility of Power7

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Joel Schopp <jschopp@austin.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>