Right now, each CPU has its own TOD. Especially, the TOD will differ
based on creation time of a CPU - e.g. when hotplugging a CPU the times
will differ quite a lot, resulting in stall warnings in the guest.

Let's use a single TOD by implementing our new TOD device. Prepare it
for TOD-clock epoch extension.

Most importantly, whenever we set the TOD, we have to update the CKC
timer.

Introduce "tcg_s390x.h" just like "kvm_s390x.h" for tcg specific
function declarations that should not go into cpu.h.
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Message-Id: <20180627134410.4901-6-david@redhat.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>