external_access: Update the way the register values are saved

Used to be incorrect unless a 16-bit binary value was used.
Now it works correctly for all values

Signed-off-by: Alistair Francis <alistair23@gmail.com>
netduinoplus2: General fixes

Signed-off-by: Alistair Francis <alistair23@gmail.com>
EXTI: Update registers after an interrupt

Signed-off-by: Alistair Francis <alistair23@gmail.com>
EXTI: Remove a debug statement

Signed-off-by: Alistair Francis <alistair23@gmail.com>