ARM64: dts: amlogic: gxbb: pinctrl: add/update UART

Add DT nodes for additional UARTs (UART B & C in EE domain) and add pins
for all EE domain UARTs.

Acked-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>