powerpc/mm/radix: Use firmware feature to enable Radix MMU

We use the existing "ibm,pa-features" device-tree property to enable
Radix MMU mode. This means we default to hash mode unless firmware tells
us it's OK to start using Radix mode.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/prom.c

@@ -166,6 +166,7 @@ static struct ibm_pa_feature {
 	 * which is 0 if the kernel doesn't support TM.
 	 */
 	{CPU_FTR_TM_COMP, 0, 0,		22, 0, 0},
+	{0, MMU_FTR_RADIX, 0,		40, 0, 0},
 };
 
 static void __init scan_features(unsigned long node, const unsigned char *ftrs,