panfrost/midgard: Always break up fragment writeout

panfrost/midgard: Always break up fragment writeout

In a fragment shader, r0 is written out with a special branch sequence.
r0 is not a real register here, but essentially a pipeline register --
as such, it needs to be written out in full and on time, with hanging
dependencies in the bundle. Otherwise, we break up the bundle, which
costs an extra ALU cycle and adds a move.

When the scheduler ran last thing, we could do this analysis within the
scheduler. Now that RA can run after scheduling, that's no longer valid,
so we remove the analysis and always break it up (at a performance
penalty). Future work can add a post-RA/post-schedule pass to merge
writeout blocks if possible. It's a bit of a low-priority next to fixing
conformance regressions, of course.

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