s390x/tcg: fix and optimize SPX (SET PREFIX)

s390x/tcg: fix and optimize SPX (SET PREFIX)

We not only invalidate the translation of the range 0x0-0x2000, we also
invalidate the translation of the new prefix range and the translation
of the old prefix range -- because real2abs would return different
results for all of these ranges when changing the prefix location.

This fixes the kvm-unit-tests "edat" test that just hangs before this
patch because we end up clearing the new prefix area instead of the old
prefix area.

While at it, let's not do anything in case the prefix doesn't change.

Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: qemu-s390x@nongnu.org
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20210805125938.74034-1-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>