msm: kgsl: Make kgsl_iommu_clocks list dynamic

Make the iommu clocks list dynamic so that we
can add new clocks to the list whenever needed.

Change-Id: I7a742c709d0bdc59d4f578329f7019959d4edb46
Signed-off-by: Nitheesh Muthuraj <nmuthuraj@codeaurora.org>