dt-bindings: gpio: fairchild,74hc595: Convert to json-schema

Convert the Generic 8-bit shift register Device Tree binding
documentation to json-schema.

Rename from gpio-74x164 to fairchild,74hc595, as the former refers to
the Linux driver, and not to a hardware name.
Add the missing hog description.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>