freedreno/a6xx: move const emit to state group

freedreno/a6xx: move const emit to state group

Eventually we want to move nearly everything, but no other state depends
on const state, so this is the easiest one to move first.

For webgl aquarium, this reduces GPU load by about 10%, since for each
fish it does a uniform upload plus draw.. fish frequently are visible in
only a single tile, so this skips the uniform uploads for other tiles.

The additional step of avoiding WFI's when using CP_SET_DRAW_STATE seems
to be work an additional 10% gain for aquarium.

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