Add a debug register

This patch uses the possibility to add a vendor-specific register and
adds a debug register useful for dumping the TIS's internal state. This
register is only active in a debug build (#define DEBUG_TIS).

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
Reviewed-by: Joel Schopp <jschopp@linux.vnet.ibm.com>
Message-id: 1361987275-26289-4-git-send-email-stefanb@linux.vnet.ibm.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>