powerpc/mm: Use a helper for finding pte bits mapping I/O area

Use a helper instead of open coding with constants. A later patch will
drop the WIMG bits and use PowerISA 3.0 defines.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/kernel/pci_64.c b/arch/powerpc/kernel/pci_64.c
index 60bb187..41503d7 100644
--- a/arch/powerpc/kernel/pci_64.c
+++ b/arch/powerpc/kernel/pci_64.c
@@ -159,7 +159,7 @@
 
 	/* Establish the mapping */
 	if (__ioremap_at(phys_page, area->addr, size_page,
-			 _PAGE_NO_CACHE | _PAGE_GUARDED) == NULL)
+			 pgprot_val(pgprot_noncached(__pgprot(0)))) == NULL)
 		return -ENOMEM;
 
 	/* Fixup hose IO resource */