iommu: msm: Support secure programming of global registers

Trustzone is now responsible for programming the global registers
of secure IOMMUs. Adjust the code to let the secure world program
the registers for secure IOMMUs. Non-secure IOMMUs will still be
programmed by us.

Change-Id: I352576c863638f241bb4ec94f53413d9d8e8266d
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>