s390x: flagify mcic values

Instead of using magic values when building the machine check
interruption code, add some defines as by chapter 11-14 in the PoP.

This should make it easier to catch problems like the missing vector
register validity bit ("s390x/kvm: Fix vector validity bit in device
machine checks"), and less hassle should we want to generate machine
checks beyond the channel reports we currently support.

Acked-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
