intel/compiler: fix 16-bit comparisons

intel/compiler: fix 16-bit comparisons

NIR assumes that booleans are always 32-bit, but Intel hardware produces
16-bit booleans for 16-bit comparisons. This means that we need to convert
the 16-bit result to 32-bit.

In the future we want to add an optimization pass to clean this up and
hopefully remove the conversions.

v2 (Jason): use the type of the source for the temporary and use
            brw_reg_type_from_bit_size for the conversion to 32-bit.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>