drm/msm/adreno: add a615 support

The Adreno A615 is used in SDM670. Add an entry to support it.

Signed-off-by: Richard Acayan <mailingradian@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/607238/


Signed-off-by: Rob Clark <robdclark@chromium.org>