[rfa] `struct _bfd' -> `struct bfd'

[Doug Evans]

Andrew Cagney writes:
 > PS, Perhaps they should (mostly) go in src/cpu/<cpu>/frv.*?

Or (for completeness' sake), src/cpu/cgen/*.

Or ...
GCC didn't use to have config/<cpu> subdirs.
They were added when config got too big.
I think it would be reasonable to just use src/cpu/frv.*
(and ditto for the other .cpu/.opc files)
until the directory became populated enough that which form
the next step took became more clear.

But in the end I have no strong opinion.

P.S. I still think .opc files should go in src/opcodes, but no matter.