msm: kgsl: Enable GPU to use multiple IOMMU devices

Set the defualt IOMMU count to two for the GPU.
If the device is 8960 (ie not 8960PRO), set the IOMMU
count to one and let kgsl take care of initializing only
one IOMMU device.

Change-Id: Iad15ba94850b5183731463443033ff37f4644630
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>