target/s390x: Remove non-architected entries from struct LowCore

target/s390x: Remove non-architected entries from struct LowCore

There are some fields in our struct LowCore which apparently have
been copied from a very old version of the Linux kernel. These
fields are not architected in the "Principles of Operation", and
only used on these memory locations in Linux kernels older than
2.6.29. Newer Linux kernels moved the entries to different locations
or are not using them at all anymore. Thus we should never access
these fields from the QEMU side, so they should be removed.

While we're at it, also add a QEMU_BUILD_BUG_ON() statement to
assert that struct LowCore has the right size.

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1551775581-27989-1-git-send-email-thuth@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>