pinctrl: meson: add g12a support

Add pinctrl support for the Amlogic G12A SoC, which is
very similar to the Amlogic AXG support but with an additionnal
drive-strength register bank.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>