PM / devfreq: arm-memlat-mon: Simplify event initialization code

Instead of repeating the event initialization code for each event, just
keep an array of events and initialize them all using a for loop.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Change-Id: Id35078953aaecb1cb0a8b64980d92e873c4e6cb5