msm: iommu: Generalize platform data for multiple targets

Make the IOMMU platform data target-independent in
preparation for adding MSM8960 IOMMU support. The IOMMU
configuration on MSM8x60 and MSM8960 is identical and the
same platform data can be used for both.

Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>