gpu: ion: Refactor platform data

Refactor platform data to allow for better
expansion in the future. Add void * for
elements unique to each heap type.

Change-Id: I435679819c67ce917b5798009eff7e71047fd2ea
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
[sboyd: drop board file changes]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>