pan/midgard: Add helpers for scheduling conditionals

pan/midgard: Add helpers for scheduling conditionals

Conditional instructions (csel and conditional branches) require their
condition to be written to a special condition pipeline register (r31.w
for scalar, r31.xyzw for vector). However, pipeline registers are live
only for the duration of a single bundle. As such, the logic to schedule
conditionals correct is surprisingly complex. Essentially, we see if we
could stuff the conditional within the same bundle as the csel/branch
without breaking anything; if we can, we do that. If we can't, we add a
dummy move to make room.

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