Where do I put my new driver?

[Alec Matthews]

I've created a new device driver that is responsible for controlling a
GPIO expander. This driver contains gpio_chip code, pinmux/pinconf,
code, pwm, and irq handlers. 

I'm not certain what I should name this driver. `pinctrl-*`, `gpio-*`,
or something else? 

I'm also not sure where this driver belongs in the source tree. Should
it exist in drivers/gpio, drivers/pinctrl, or drivers/pwm?

I have developed this driver out of tree, now I am trying to move it in
tree so I can begin the patch process. I appreciate any insight that
this list may have on where it belongs.