freedreno/a6xx: Drop the WFI in constant uploads.

freedreno/a6xx: Drop the WFI in constant uploads.

Now that the bin vs render constlen is fixed, we can skip these waits.

Improves webgl aquarium performance at 10k fish from 27fps to 33.
Some highlights from renderdoc-traces:

traces/android/minecraft.rdc:             +17.1% +/-   3.4%
traces/glmark2/ideas-speed=duration.rdc:  +11.6% +/-   2.4%
traces/android/candycrush.rdc:            +5.4%  +/-   1.1%
traces/android/clashofclans.rdc:          +4.4%  +/-   1.3%

Reviewed-by: Rob Clark <robdclark@gmail.com>