So is there a simple way of attaching and ISR to a GPIO from user code?
You need to think like you were using Linux: No interrupt handling in user code! This needs to go into your board logic. Expecially if you are customizing the board to some non-off-the-shelf configuration with additional hardware. You custom logic should not be included in generic board configurations.
You would do this by copying the board code that you want and putting in your directory out-of-tree. The set up the CUSTOM BOARD configuration options in boards/Kconfig.
