gpu: ion: Actually return aligned memory

Currently, the ion allocation API takes an alignment
argument. This alignment argument is currently ignored
everywhere. The system heaps cannot support the alignment
argument, but carveout heaps can. Add support for carveout
heaps to give back aligned memory.

Change-Id: Ic4cff37a7de51e1c85e273c2589958f7f13c33c9
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>