ARM64: dts: meson-gxl: Add pinctrl nodes

Add pinctrl nodes and pin definitions for Amlogic Meson GXL.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
[khilman: use GXBB include until GXL pinctrl support merged]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>