msm: kgsl: Add back apriv bit for legacy targets

Commit ef5440e7 ("msm: kgsl: Remove nonsense around the a5xx and a6xx
SMMU table update") removed a lot of the cruft around a pagetable update
but unfortunately legacy targets still needed APRIV to write to the
pagetable_desc memory so add that part back in.

Change-Id: Ic0dedbad71544eaaf77efe1d523c9bf533cb4973
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>