Don't compile some opcodes files when bfd is 32-bit only

[Jim Wilson]

On Thu, Dec 2, 2021 at 2:02 PM Alan Modra via Binutils <
binutils@sourceware.org> wrote:

> Reverting the opcodes Makefile changes will currently result in
> opcodes failing to link.  The riscv opcodes objects now depend on
> riscv bfd objects that are only compiled for a 64-bit bfd.
>

Nelson Chu submitted a patch Nov 12 to fix 32-bit riscv32 builds, but at
the time the patch didn't seem necessary.  I think this should be
revisited.  I think this patch would fix some of these issues people are
having with 32-bit enable-targets=all builds.
https://sourceware.org/pipermail/binutils/2021-November/118498.html

Jim