cores: AVR_IOPORT_DECLARE

convert port sructure declarations to macro AVR_IOPORT_DECLARE.

modified:   simavr/cores/sim_90usb162.c
modified:   simavr/cores/sim_mega128.c
modified:   simavr/cores/sim_mega1280.c
modified:   simavr/cores/sim_mega1281.c
modified:   simavr/cores/sim_mega128rfa1.c
modified:   simavr/cores/sim_mega128rfr2.c
modified:   simavr/cores/sim_mega169.c
modified:   simavr/cores/sim_mega2560.c
modified:   simavr/cores/sim_megax.h
modified:   simavr/cores/sim_tiny2313.c
modified:   simavr/sim/avr_ioport.h