drm/msm/a6xx: add GMU_CX_GMU_CX_FALNEXT_INTF write for a650

downstream msm-5.14 kernel added a write to this register, so match that.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20210608172808.11803-4-jonathan@marek.ca


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