s390x/tcg: simplify machine check handling

s390x/tcg: simplify machine check handling

We currently only support CRW machine checks. This is a preparation for
real floating interrupt support.

Get rid of the queue and handle it via the bit INTERRUPT_MCHK. We don't
rename it for now, as it will be soon gone (when moving crw machine checks
into the flic).

Please note that this is the same way also KVM handles it: only one
instance of a machine check can be pending at a time. So no need for a
queue.

While at it, make sure we try to deliver only if env->cregs[14]
actually indicates that CRWs are accepted.

Drop two unused defines on the way (we already have PSW_MASK_...).

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180129125623.21729-5-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>