msm: ipa4: Add IPA clock-gated case in IPA PM

Add an API to change clk_scaling vote in pm_ctx for pm_stats.
Change this value to zero when we disable IPA clks.

Change-Id: I7a016cdf89904f4d5ecbfd9b9afbd05fbfe6244b
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>