freedreno/ir3: move const_state back to variant

freedreno/ir3: move const_state back to variant

For shader-cache, we want to not have anything important in `ir3_shader`.
And to have shader variants with lower const size limits (to properly
handle cross-stage limits), we also want variants to be able to have
their own const_state.

But we still need binning pass shaders to align with their draw pass
counterpart so that the same const emit can be used for both passes.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5508>