ARM: rockchip: add debug uart used by rk3288

The uarts on rk3288 are still compatible with the dw_8250, but located
at a different position and need DEBUG_UART_8250_WORD enabled.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Tested-by: Will Deacon <will.deacon@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>