Tidy up address/pointer handling, with silent flag setting.

	* avr-tdep.c (avr_make_code_addr): Cleared coding.
	(avr_make_code_ptr): Enable function.
	(avr_make_data_addr): Clearer coding.
	(avr_make_data_ptr): Enable function.
	(avr_address_to_pointer): Silently set bits.
	(avr_pointer_to_address): Likewise.
	(avr_integer_to_address): Likewise.
	(avr_addr_bits_remove): Created.
	(avr_read_pc): Use avr_make_code_addr.
	(avr_unwind_pc): Likewise.
	(avr_gdbarch_init): Set avr_addr_bits_remove.