msm: kgsl: Switch to using the dmabuf APIs

The dmabuf APIs are now fully supported upstream. Since Ion
is now a dmabuf exporter, there is no need to call those APIs
directly. Switch to calling the dmabuf APIs to generate
scattergather lists for mapping to be more compatible.

Change-Id: Ie393e74bba080cba8a10e60908af7932729e6da6
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>