drm/msm/a5xx: Add support for Adreno 508, 509, 512 GPUs

The Adreno 508/509/512 GPUs are stripped versions of the Adreno
5xx found in the mid-end SoCs such as SDM630, SDM636, SDM660 and
SDA variants; these SoCs are usually provided with ZAP firmwares,
but they have no available GPMU.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Tested-by: Martin Botka <martin.botka1@gmail.com>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>