msm: pm: export msm_pm_collapse

Currently cpu_suspend() API takes 2 arguments as input
where one of the argument used as a suspend finisher.
Suspend finisher function takes care of handing over
the control to TZ after doing the necessary house
keeping of core states. On latest ARM based targets
cpu_suspend() API is modified and it accepts only
a single argument and suspend finisher is registered
as cpu_ops at boot time.

Change-Id: Ibbb952ff182418c30ad76c9ff0b47e432860f0e7
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>