soc: qcom: ssr: Add dependency hooks for subsystem power operations

The subsystems might depend on other subsystem's state to be powered-on
or powered-off. Hence, add flexibility via 'pon-depends-on' and
'poff-depends-on' device-tree properties. This way, first the dependent
subsystem's power operation would be fulfilled and then this
subsystem's.

Change-Id: I9764178ff9cc3957389f25cb5b0882c75c0d7db0
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>