msm: kgsl: Turn on additional clock for IOMMU

Turn on an additional clock for IOMMU if it is valid. This additional
clock is present on devices which have the IOMMU unit access tied to
the core clock of another component. This has been introduced from
IOMMU-v2 onwards.

Change-Id: I8b0a0f23cb789d820a8d515cae54b44f556e634d
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>
Signed-off-by: Rajeev Kulkarni <krajeev@codeaurora.org>