powerpc: Get USE_STRICT_MM_TYPECHECKS working again

The typesafe version of the powerpc pagetable handling (with
USE_STRICT_MM_TYPECHECKS defined) has bitrotted again.  This patch
makes a bunch of small fixes to get it back to building status.

It's still not enabled by default as gcc still generates worse
code with it for some reason.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/init_64.c

@@ -228,8 +228,8 @@ int __meminit vmemmap_populate(struct page *start_page,
 			start, p, __pa(p));
 
 		mapped = htab_bolt_mapping(start, start + page_size, __pa(p),
-					   PAGE_KERNEL, mmu_vmemmap_psize,
-					   mmu_kernel_ssize);
+					   pgprot_val(PAGE_KERNEL),
+					   mmu_vmemmap_psize, mmu_kernel_ssize);
 		BUG_ON(mapped < 0);
 	}