rockchip: px30: Add support for UART3 as serial output

Add the UART3 base definition for serial output, which is used on some
PX30 SoM boards.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Change-Id: I8490b15c9f129a33c01cb78bd78675014bc7b015
1 file changed