Change return type from void to int. Check the combination
of operands, return 1 if valid. Fix to avoid BUF overflow.
Report undefined combinations of operands in COMMENT.
Report internal errors to stderr. Output the adiw/sbiw
constant operand in both decimal and hex.
(print_insn_avr): Disassemble ldd/std with displacement of 0
as ld/st. Check avr_operand () return value, handle invalid
combinations of operands like unknown opcodes.
