drm/msm: registers: Add GMU FW version register

Add a register that contains the GMU core firmware version on non-
legacy (non-sdm845-family) SoCs.

The name is guesstimated based on what it does downstream, but it'll
do.

Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/629932/


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