clk: qcom: Add support for spm event pll management

SPM event will be asserted/de-asserted when SR2 PLL is disabled/enabled.
This is required so as the SPM hardware could take care of turning on/off
the PLL when APSS moves to low power mode.

Change-Id: Ic6aa18e47eb352a3582f5e278d7bd99e02bdbcfd
Signed-off-by: Taniya Das <tdas@codeaurora.org>