kvx_dis_init

kvx_dis_init currently always returns true, but error conditions do so
by "return -1" which converts to true.  The return status is ignored
anyway, and it doesn't make much sense to error on unexpected arch or
mach:  If print_insn_kvx is called then the atch is known to be kvx,
and it's better to choose some default for a user passing an unknown
mach value rather than segfaulting in decode_insn when env.opc_table
is NULL.

I've chosen the default mach to be bfd_mach_kv3_1, the default in
bfd/cpu-kvx.c, not that it matters very much.  In normal objdump/gdb
usage, info->mach won't be an unexpected value.

	* kvx-dis.c (kvx_dis_init): Return void.  Don't error on
	unexpected arch or mach.  Default to bfd_mach_kv3_1 for
	unknown mach.  Don't clear info->disassembler_options.