freedreno/ir3: drop deref nodes

freedreno/ir3: drop deref nodes

The meta-deref instruction doesn't really do what we need for relative
destination.  Instead, since each instruction can reference at most a
single address value, track the dependency on the address register via
instr->address.  This lets us express the dependency regardless of
whether it is used for dst and/or src.

The foreach_ssa_src{_n} iterator macros now also iterates the address
register so, at least in SSA form, the address register behaves as an
additional virtual src to the instruction.  Which is pretty much what
we want, as far as scheduling/etc.

TODO:
For now, the foreach_src{_n} iterators are unchanged.  We could wrap
the address in an ir3_register and make the foreach_src_{_n} iterators
behave the same way.  But that seems unnecessary at this point, since
we mainly care about the address dependency when in SSA form.

Signed-off-by: Rob Clark <robclark@freedesktop.org>