arc: Update bfd arc pattern file to allow enable-targets=all

arc: Update bfd arc pattern file to allow enable-targets=all

The ARC backend uses a BFD pattern file to generate three ARC targets:
- an BFD ARC target for ARCv1 and ARCv2 CPU families. It also works
for big-endian variants.
- an BFD ARC64 target for ARCv3 64bit machines. It also allows working
with ARCv3 32bit machines.
- an BFD ARC32 target for ARCv4 32bit machines. It also allows working
with ARCv3 64bit machines.

When configuring with `--enable-targets=all` some patterns are defined
multiple times. Fix this issue.

Signed-off-by: Claudiu Zissulescu <claziss@gmail.com>