pinctrl: amlogic: gxbb: add more UART pins

Add EE domain pins for UART A, B & C.

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