serial: sh-sci: Add SCIFA/B SCPCR register definitions

Add the register definitions for the Serial Port Control and Data
Registers on SCIFA/SCIFB, which are needed for RTS/CTS pin control.

Extracted from patches by Magnus Damm <damm+renesas@opensource.se>.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>