pinctrl: meson-axg: Add new pinctrl driver for Meson AXG SoC

Add new pinctrl driver for Amlogic's Meson-AXG SoC.

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Xingyu Chen <xingyu.chen@amlogic.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>