opcodes/avr: Implement style support in the disassembler

	* disassemble.c: (disassemble_init_for_target): Set
	created_styled_output for AVR based targets.
	* avr-dis.c: (print_insn_avr): Use fprintf_styled_ftype
	instead of fprintf_ftype throughout.
	(avr_operand): Pass in and fill disassembler_style when
	parsing operands.