FDT bindings document for gpio-i2c devices.
Using the gpio_pin_* functions to acquire/release/manipulate gpio pins
removes the constraint that both gpio pins must belong to the same gpio
controller/bank, and that the gpioiic instance must be a child of gpiobus.
Removing those constraints allows the driver to be fully compatible with
the modern dts bindings for a gpio bitbanged i2c bus.
For hinted attachment, the two gpio pins still must be on the same gpiobus,
and the device instance must be a child of that bus. This preserves
compatibility for existing installations that have use gpioiic(4) with hints.
gpioled(4).
Tested on RPi and BBB (using the hardware I2C controller and gpioiic(4) for
the I2C tests). It was also verified for regressions on RSPRO (MIPS/ar71xx)
used as reference for a non OFW-based system.
Update the gpioled(4) and gpioiic(4) man pages with some details and
examples about the FDT/OFW support.
Some compatibility details pointed out by imp@ will follow in subsequent
commits.
Approved by: adrian (mentor, implicit)
