Make the 2560 PORTE/0 pin change interrupt visible as it mostly works.

Make the 2560 PORTE/0 pin change interrupt visible as it mostly works.
Add the missing pin change interrupts for 1280 and 1281.

In avr_ioport.[ch], fix multiple causes (but not all) of
mis-triggering of pin change interrupts including upstream issue #343:
Pin change interrupts incorrectly fire when a timer compare event occurs.
Other causes are initial setting of DDR and the AVR_IOPORT_OUTPUT bit.

Move the mask and shift data for ATmega2560 into the ioport structure.

Add a test for pin change interrupts.