s390: add support for IBM zBC12 machine

Just add the new model number where appropiate.

Cc: stable@vger.kernel.org # v3.10
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/init.c

@@ -69,6 +69,7 @@ static void __init setup_zero_pages(void)
 		order = 2;
 		break;
 	case 0x2827:	/* zEC12 */
+	case 0x2828:	/* zEC12 */
 	default:
 		order = 5;
 		break;