drm/msm: a6xx: Use WHERE_AM_I for eligible targets

Support the WHERE_AM_I opcode for the A618, A630 and A640 GPUs if the
microcode supports it. The WHERE_AM_I opcode allows the RPTR shadow
to be updated in priviliged memory which protects the shadow from being
read or written from user submissions.

A650 already supports extended APRIV have built in hardware support for
to access privilged memory from the CP and can go back to using the
hardware RPTR shadow feature.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>