* I2C address for the panel regulator driver depends on the device and
DSI port the display is connected on. Add more backlight paths to support
different hardware configurations. Also add path for legacy rpi_backlight
driver to make testing easier.
* Old rpi_backlight driver is no longer used on recent kernel versions.
Regulator driver is used for backlight instead.
* Change the backlight path and implement scaling to support the official
Raspberry Pi 7" DSI Touch Display & Touch Display 2.
* The original Touch Display has max brightness of 255 while the new Touch
Display 2 has 31.
