STM32F405: Rename all of the original files

This is a messy commit, there are other changes inside the files

Signed-off-by: Alistair Francis <alistair23@gmail.com>
stn32f405_exti: Add the external interrupt device

Signed-off-by: Alistair Francis <alistair23@gmail.com>
Netduino: Connect the EXTI device with the GPIO

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