s390: add zEC12 code generation support

Allow to generate code that only runs on zEC12 machines.

Also add a check which prevents the kernel to run on machines which
do not have any of the following new facilities installed:

- (48) decimal-floating-point zoned-conversion
- (49) execution-hint
- (49) load-and-trap
- (49) miscellaneous-instruction-extensions
- (49) processor-assist
- (50) constrained transactional-execution
- (73) transactional-execution

48, 49, 50 and 73 are the bit numbers of the facility indications for
each of the required facilities.

Note that we assume that user-space gets compiled with the same
compiler options, therefore we also test for a dfp facility even
if the kernel doesn't make use of it.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index cfdad57..2568590 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -1006,6 +1006,9 @@
 	case 0x2818:
 		strcpy(elf_platform, "z196");
 		break;
+	case 0x2827:
+		strcpy(elf_platform, "zEC12");
+		break;
 	}
 }