Pinmux-helper

Add a helper to configure the pinmux.

I've tested the ability to configure the pinmux and unload the slot (using 1st commit), but there is an additional bug-fix to handle unloading the wrong slot number that I haven't yet tested (2nd commit).

Just wanted to get this pull request in so you know that it is here. I'll come back with the testing status once the kernel is built and loaded onto my board.