panfrost/midgard: Handle csel correctly

panfrost/midgard: Handle csel correctly

We use an algebraic pass for the csel optimizations, and use proper
vectorized csel ops (i/fcsel_v) for mixed, rather lowering.

To avoid regressions along the way, we fix an issue with the copy
propagation pass (it should not attempt to propagate constants).
Similarly, we take care to break bundles when using csel to fix some
scheduler corner cases.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>