kmemleak : Make module scanning optional using config

Currently kmemleak scans module memory as provided
in the area list. This takes up lot of time with
irq's and preemption disabled. Provide a compile
time configurable config to enable this functionality.

Change-Id: I5117705e7e6726acdf492e7f87c0703bc1f28da0
Signed-off-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>