powerpc: Get the number of SLBs from "slb-size" property

The PAPR says that the property for specifying the number of SLBs should
be called "slb-size".  We currently only look for "ibm,slb-size" because
this is what firmware actually presents.

This patch makes us look for the "slb-size" property as well and in
preference to the "ibm,slb-size".  This should future proof us if
firmware changes to match PAPR.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/prom.c

@@ -590,6 +590,11 @@ static void __init check_cpu_slb_size(unsigned long node)
 {
 	u32 *slb_size_ptr;
 
+	slb_size_ptr = of_get_flat_dt_prop(node, "slb-size", NULL);
+	if (slb_size_ptr != NULL) {
+		mmu_slb_size = *slb_size_ptr;
+		return;
+	}
 	slb_size_ptr = of_get_flat_dt_prop(node, "ibm,slb-size", NULL);
 	if (slb_size_ptr != NULL) {
 		mmu_slb_size = *slb_size_ptr;