(CGEN_ATTR): Make unsigned char.
(CGEN_ATTR_TYPE): Update.
(CGEN_ATTR_{ENTRY,TABLE}): New types.
(cgen_base): Move member `attrs' to cgen_insn.
(CGEN_KEYWORD): New member `null_entry'.
(CGEN_{SYNTAX,FORMAT}): New types.
(cgen_insn): Format and syntax separated from each other.