Force 16 byte alignment of preloaded files on i386 and amd64.

[markj]

Summary

This is required to support early microcode loading, which occurs before
we can use a kernel memory allocator to make an aligned copy of the
microcode update file.

[markj]

The approach taken in D16370 means that we don't need this anymore. There is some argument for providing a minimum alignment of CACHE_LINE_SIZE or so to all preloaded files, but this change isn't the right way to do that.