coresight: tmc: Add IOMMU support to TMC ETR

This adds IOMMU support to the TMC ETR driver. The IOMMU support helps
with contiguous VA usage for physically scattered memory and hence avoids
the need for native scatter gather mode usage in the TMC ETR driver.
It also helps with sandboxing TMC ETR and hence protecting the system from
erroneous TMC ETR accesses.

Change-Id: I17237bc02924e475c3fb324347734d01f72cc797
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>