drivers: serial: add Renesas R-Car driver This patch add support for polling based UART on the Renesas R-Car SCIF (Serial Communication Interface with FIFO) This hardware block can be found on various Renesas R-Car SoC series. It allows to get console on R-Car Gen3 H3ULCB board. Signed-off-by: Aymeric Aillet <aymeric.aillet@iot.bzh>