These H3 boards all expose UART1-3 on their expansion header. Since
other functions can be muxed to these pins, they are explicitly
disabled. To enable them, one could use DT overlays or U-boot commands:

 => fdt set /soc/serial@01c28c00 status okay
Signed-off-by: Jorik Jonker <jorik@kippendief.biz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>