hw/s390x: tod: make explicit checks for accelerators when initializing

hw/s390x: tod: make explicit checks for accelerators when initializing

replace general "else" with specific checks for each possible accelerator.

Handle qtest as a NOP, and error out for an unknown accelerator used in
combination with tod.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Signed-off-by: Cho, Yu-Chen <acho@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210707105324.23400-4-acho@suse.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>