Convert the ingenic,pinctrl.txt doc file to ingenic,pinctrl.yaml.

In the process, some compatible strings now require a fallback, as the
corresponding SoCs are pin-compatible with their fallback variant.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200622113740.46450-1-paul@crapouillou.netSigned-off-by: Linus Walleij <linus.walleij@linaro.org>