tests: add testcase for TCO watchdog emulation

This patch adds a testcase that covers the following:
  1) TCO default values
  2) first and second TCO timeout
  3) watch and validate ticks counter through TCO_RLD register
  4) maximum supported TCO timeout (0x3ff)
  5) watchdog actions (pause/reset/shutdown/none) upon second TCO
     timeout
  6) set and get of TCO control and status bits

MST: The test does not pass yet, so it's disabled by default.

Signed-off-by: Paulo Alcantara <pcacjr@zytor.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
