coresight: support sdc regulators without voltage/current levels

Add support for sdc regulators that don't have voltage or current
levels. This will allow tpiu output via sdc connector on chips
that power sdc connector with regulators without voltage and
current level support.

Change-Id: I03e9e94aebef3fc54a59922c50743ea8624bfdcf
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>