Do not use hardcoded literals in halide_malloc.
Do not use hardcoded literals in halide_malloc.

Also add some new meaningful comments to describe what is goign on.

tdenniston/Halide,jiawen/Halide,ronen/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,ronen/Halide,tdenniston/Halide,tdenniston/Halide,tdenniston/Halide,ronen/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,tdenniston/Halide,tdenniston/Halide,tdenniston/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,jiawen/Halide,ronen/Halide,ronen/Halide,psuriana/Halide,jiawen/Halide,ronen/Halide,tdenniston/Halide,jiawen/Halide,ronen/Halide,jiawen/Halide,kgnk/Halide,ronen/Halide,jiawen/Halide,psuriana/Halide,jiawen/Halide