more descriptions

See merge request !1

The SX126x repo was moved to the SudoMaker organization. Update the name and the link of the repo in README and submodule.

This driver was previously using the SYSFS API to interact with GPIO. This API is deprecated since kernel 4.8 but was still working up to 5.10. The SYSFS API was removed in more recent version and is now replaced by a character device interface.

In this commit, I replaced calls to the old SYSFS API to this new GPIO interface. I also added a small test program to test GPIO (display info about all GPIO chips and tries to detect the gpiochip corresponding to the CH341 of the USB adapter).

Also, the initialization of the SPI bus now binds to spidev driver since this is needed to make /dev/spidevx.y available since kernel 5.1.