nir+ir3: address calculation optimizations (2nd approach)

Alternative approach to !2141 (closed)

This introduces an amul instruction to be used in address calculation, rather than directly using imul. For drivers that don't set has_imul24, these will be converted to imul. Drivers that do have imul24 should call the new nir_lower_amul() pass which will lower the amuls to either imul24 or imul depending on whether signed 24b math is sufficient to construct an offset.

Still needs some patch cleanup.. but I think overall I like this better than !2141 (closed), and it does handle more cases (with slightly better shader-db numbers as a result). It would be a bit nicer if (a) register access was also intrinsics, and (b) we had a generic(ish) way to identify offset and block-id parameters to intrinsics. (Or maybe if the src parameter orders were better aligned.)

total instructions in shared programs: 8693021 -> 8666432 (-0.31%)
instructions in affected programs: 171704 -> 145115 (-15.49%)
helped: 746
HURT: 0

total full in shared programs: 364087 -> 364007 (-0.02%)
full in affected programs: 815 -> 735 (-9.82%)
helped: 89
HURT: 3