Wake-up/Bootloader/User Button

This button is required for:

Wake-up of the device from low power sleep modes as most devices offer a special pin(s) for this purpose
Entering bootloader mode of the target
Other user interaction, this is not the main reason why we have the button but when we have it we can use it for other purposes as well

It is important that the above functions are covered by corresponding pins on the target that offer these features because then the user experience is the same across the whole Xplained Pro platform.