drm/msm/adreno: Simplify read64/write64 helpers

The _HI reg is always following the _LO reg, so no need to pass these
offsets seprately.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/511581/
Link: https://lore.kernel.org/r/20221114193049.1533391-2-robdclark@gmail.com