PM / OPP: Add light weight _opp_free() routine

The OPPs which are never successfully added using _opp_add() are not
required to be freed with the _opp_remove() routine, as a simple kfree()
is enough for them.

Introduce a new light weight routine _opp_free(), which will do that.

That also helps us removing the 'notify' parameter to _opp_remove(),
which isn't required anymore.

Note that _opp_free() contains a call to _remove_opp_table() as the OPP
table might have been added for this very OPP only. The
_remove_opp_table() routine returns quickly if there are more OPPs in
the table. This will be simplified in later patches though.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>