OPP: Use consistent names for OPP table instances

The OPP table is called "opp_table" at most of the places and "table" at
few. Make all of them follow the same naming convention, "opp_table".

Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>