WIP: freedreno: add tgsi lowering pass

Currently lowers the following instructions:

   DST, XPD, SCS, LRP, FRC, POW, LIT, EXP, LOG, DP4,
   DP3, DPH, DP2

translating these into equivalent simpler TGSI instructions.
WIP: freedreno/compiler/a3xx: remove lowered instructions
WIP: freedreno/a3xx/compiler: compiler cleanups

Drop color/pos/psize_regid, plus a few compiler and IR cleanups.
WIP: freedreno: resync generated headers
WIP: freedreno/a3xx: fix const confusion

Gallium can leave const buffers bound above what is used by the current
shader.  Which can have a couple bad effects:

1) write beyond const space assigned, which can trigger HLSQ lockup
2) double emit of immed consts, first with bound const buffer vals
followed by with actual immed vals.  This seems to be a sort of
undefined condition.
WIP: freedreno/a3xx: handle frag z write
WIP: freedreno/a3xx: add logicop