nir: Make boolean conversions sized just like the others

Instead of a single i2b and b2i, we now have i2b32 and b2iN where N is
one if 8, 16, 32, or 64.  This leads to having a few more opcodes but
now everything is consistent and booleans aren't a weird special case
anymore.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/compiler/nir/nir.h

@@ -1568,8 +1568,8 @@ nir_alu_instr_is_comparison(const nir_alu_instr *instr)
    case nir_op_uge:
    case nir_op_ieq:
    case nir_op_ine:
-   case nir_op_i2b:
-   case nir_op_f2b:
+   case nir_op_i2b32:
+   case nir_op_f2b32:
    case nir_op_inot:
    case nir_op_fnot:
       return true;