drm/msm/a6xx: Some reg64 conversion

The next generated header update will drop the _LO/_HI suffix, now that
the userspace tooling properly understands 64b vs 32b regs (and the _LO/
_HI workarounds are getting cleaned up).  So convert to using the 64b
reg helpers in prep.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/527923/
Link: https://lore.kernel.org/r/20230320185416.938842-1-robdclark@gmail.com