gpu: ion: Add Tracepoints to iommu/system heap

Add trace events to kmem.h and set up trace points in ion/system
heap to keep track of information pertaining to page allocations.

Change-Id: I35c0bd1c0c2032dba6ea80b060b05bdb847d58ad
Signed-off-by: Adrian Alexei <aalexei@codeaurora.org>