OPP: Introduce dev_pm_opp_get_freq_indexed() API

[ Upstream commit 5f756d03 ]

In the case of devices with multiple clocks, drivers need to specify the
frequency index for the OPP framework to get the specific frequency within
the required OPP. So let's introduce the dev_pm_opp_get_freq_indexed() API
accepting the frequency index as an argument.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[ Viresh: Fixed potential access to NULL opp pointer ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Stable-dep-of: b44b9bc7cab2 ("OPP: fix dev_pm_opp_find_bw_*() when bandwidth table not initialized")
Signed-off-by: Sasha Levin <sashal@kernel.org>