OPP: Don't set OPP recursively for a parent genpd

Like other frameworks (clk, regulator, etc.) genpd core too takes care
of propagation to performance state to parent genpds. The OPP core
shouldn't attempt the same, or it may result in undefined behavior.

Add checks at various places to take care of the same.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>