math, crypto, hash: Write power64 versions of assembler routines where applicable

<pre>We want to write power64 versions of the assembler routines in the math package, in
several crypto packages, and in the hash/crc32 package.  For each of those packages
where we have .s files, we should either write a power64 version or determine that the
Go version is as good as we can write in assembler.</pre>
