iommu: msm: Add support for alt_core_clk for IOMMU

Some of the IOMMUs might require an extra clock to allow programming
of the IOMMU registers. Add support for an alternative core clock so
that the correct clocks can be enabled before accessing IOMMU
registers.

Change-Id: Ie79fcf7ddca0080c6938f0d28eea61a6c33b949c
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>