freedreno/ir3: moar better scheduler

freedreno/ir3: moar better scheduler

Add a new pass that inserts additional dependencies, rather than simply
relying on SSA srcs added in the nir->ir3 frontend.  This makes it
easier to deal with barriers, but the additional false deps also lets us
deal properly with ensuring a write depends on all previous reads.

Since conversion to barrier instructions is lossy (ie. just knowing the
instruction doesn't tell us enough about what other instructions the
barrier applies to), use barrier_class/barrier_conflict fields in the
ir3_instruction to retain this information.

This could probably be relaxed somewhat by considering *which* array/
buffer/image variable is being referenced.  Ie. a write to buffer A
can overtake a read from buffer B, if B is not coherent.  (right?)

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