dt-bindings: gpio: pca95xx: add entry for pcal6534 and PI4IOE5V6534Q

The NXP PCAL6534 is a 34-bit I2C I/O expander similar to the PCAL6524. The
Diodes PI4IOE5V6534Q is a functionally identical chip provided by Diodes
Inc.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>