gpu: ion: Add scm calls for content protection 2.0

The next generation of content protection has separate SCM
calls into TZ. Add these functions in a dedicated file so they
can be used by any Ion heap.

Change-Id: I197130f6a5fc33efcd6871b0f7c362fa99f18d20
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>