rockchip: Streamline and complete UARTn_BASE macros.

In order to set the UART base during bootup in common code of
plat/rockchip, we need to streamline the way the UART base addresses
are defined and add the missing definitions and mappings.

This patch does so by following the pattern UARTn_BASE, which is
already in use on RK3399 and RK3328. The numbering itself is derived
from the upstream Linux DTS files of the individual SoCs.

Signed-off-by: Christoph Müllner <christophm30@gmail.com>
Change-Id: I341a1996f4ceed5f82a2f6687d4dead9d7cc5c1f