gpu: ion: Move ION_HEAP_TYPE_DMA to msm specific code

ION_HEAP_TYPE_DMA has not yet been merged upstream. Keep
the definitions in msm code until a final version has
been reached.

Change-Id: Idaf3a4df48a627f94d60c53d30edc7a20b1b2127
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>