Use devicetree overlay so we can properly map the reset GPIO with gpiod

[al177]

Recent (6.somethingorother) kernels removed the legacy GPIO interface we used for controlling the ESP8089 reset from the Pi (or other platform). For now there's a hackish method in place to use a deprecated but not-yet-axed GPIO interface called libgpio, but this hack makes the driver Pi-specific and we can't expect that libgpio will be around for long (commit 4865180).

Create a Devicetree overlay for Raspberry Pi that can be installed alongside the DKMS, and be used as a template for other platforms. Update sdio_stub.c reset function to use gpiod instead of libgpio.