gpu: ion: Add check for overlapping heaps

During bootup add check to ensure heap addresses are not overlapping
with each other. If a heap is found to be overlapping with another
heap boot will be stopped with a call to panic.

Change-Id: Id37aefa2e09aa165ec376e241e282faf5f3c5737
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>