pinctrl: Fix gpio/pin mapping for Meson8b

The num_pins field in the struct meson_domain_data must include also the
missing pins in the Meson8b SoC, otherwise the GPIO <-> pin mapping is
broken on this platform. Avoid also the dinamic allocation for GPIOs.

Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>