msm: pm: Support SPM PLL management

CPU PLLs can be turned off when the last core running off that PLL enters
power collapse. Skip software clock management in the driver if
qcom,saw-turns-off-pll is set.

Change-Id: I77c52481c9ec4834ac6b7c0355e41069e2e354d6
Signed-off-by: Karthik Parsha <kparsha@codeaurora.org>