PM / devfreq: disable certain interrupts events

As per the current algorithm the driver is only interested
in interrupts arising due to certain thresholds being crossed.
Program interrupt registers such that only those interrupts are
handled and the rest are ignored.

Change-Id: I8e344c28967a36f96116db5c1e8a2aa00883e948
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>