msm: kgsl: Initialize only required IOMMU context

Enforce initialization of user and private contexts only.
Only these contexts are used for both IOMMU v1 and v2.
Ignore additional contexts that may be defined for graphics
in the board or dts file.

Change-Id: Ib2a903f851421c4ac2c17b5aa9d822108ec6813b
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>