iommu: pass proper vmid value for secure attachments

Pass the proper VMID value during secure attach. This VMID is used by
the HYP/TZ to maintain the pagetables.

Change-Id: I3b7c27c079b044c9325bcbcb6fa4312e424f3a94
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>