* config/tc-m68k.c (m68k_index_width_default): New static
variable.
(m68k_ip): Use m68k_index_width_default to set the size of a base
register whose size was not given.
(md_longopts): Add --base-size-default-16 and
--base-size-default-32.
(md_parse_option): Handle new options.
(md_show_usage): Mention new options.
* doc/c-m68k.texi (M68K-Opts): Document new options.
