drm/msm: Signal fences sooner

Nothing we do to in update_fences() can't be done in an atomic context,
so move this into the GPU's irq context to reduce latency (and call
dma_fence_signal() so we aren't relying on dma_fence_is_signaled() which
would defeat the purpose).

Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20210726144359.2179302-3-robdclark@gmail.com


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