msm: kgsl: Keep vote on clocks while programing SMMU

SMMU clocks should be enabled when accessing smmu registers. So keep a
vote on smmu clocks while programing QSMMU workaround. Also, keep smmu
clocks enabled through out kgsl_iommu_start() to avoid unnecessary
latencies due to multiple toggling of these clocks.

Change-Id: I2d0a4590d5969db8fe8ef063c841b7457268c999
Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>