msm: kgsl: Increment the map statistics

Increase the number of entries mapped to a pagetable when a
map occurs. This statistic is displayed when a mapping error
occurs and is useful for debug.

Change-Id: Icff5975755555d599a056cea0694be608b26fa08
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>