opcodes: handle bfd_amdgcn_arch in configure script

There isn't an actual opcodes implementation for the AMDGCN arch (yet),
this is just the bare minimum to get

  $ ./configure --target=amdgcn-hsa-amdhsa --disable-gas
  $ make all-binutils

working later in this series.

opcodes/ChangeLog:

	* configure.ac: Handle bfd_amdgcn_arch.
	* configure: Re-generate.

Change-Id: Ib7d7c5533a803ed8b2a293e9275f667ed781ce79
3 files changed