msm: kgsl: Expose some of the internal IOMMU functions

Define static inline functions that call some of the internal IOMMU
functions via function pointers. These functions are used when in
stream pagetable updates will be performed for IOMMU, and need to
be called from a file other than kgsl_iommu.c

Change-Id: I023a6b5442742fd9184f66d6f2bb05dc75cea8ea
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>