pinctrl: meson: remove offset from pinctrl

Offset on meson pinctrl and gpios is something that was carried from the
vendor driver, where there is a weird link between the 2
controllers. Since these 2 controllers are independent, this offset adds
an unnecessary complexity.

This patch remove this manually set offset and rely on pinctrl to figure
out the gpio base offset

Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>