Use /lib/efi/{x32,x64} for storing EFI binaries

Use /lib/efi/{x32,x64} for storing EFI binaries

- /lib seems better than /usr/lib for such lowlevel services, separate
  /usr is considered obsolete anyway.
- do not use /lib64 for 64-bit binaries, as /libx64 is not available on
  32-bit PLD, but 64-bit EFI binaries may be needed to boot 32-bit PLD
  from a 64-bit EFI platform. Instead x32 and x64 subdirectories are
  provided ('x64', 'x32' is the notation often used in EFI environmnet)