gpu: ion: Add support for CMA allocations in cp heap

Extend the cp heap to allow memory to be allocated from
the contiguous memory allocator (CMA) instead of from
the standard carveout region. The option to use CMA or regular
carveout memory is configured via a parameter in platform
data.

Change-Id: Ie26a867f8355280b4086afd7631a934a7c4b1e21
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>