opp: Expose of-node's name in debugfs

[ Upstream commit 021dbeca ]

It is difficult to find which OPPs are active at the moment, specially
if there are multiple OPPs with same frequency available in the device
tree (controlled by supported hardware feature).

Expose name of the DT node to find out the exact OPP.

While at it, also expose level field.

Reported-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>