serial: sh-sci: Add r8a77990 support

This patch adds the R-Car E3 serial documentation.
Signed-off-by: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/renesas,sci-serial.txt

@@ -54,6 +54,8 @@ Required properties:
     - "renesas,hscif-r8a77970" for R8A77970 (R-Car V3M) HSCIF compatible UART.
     - "renesas,scif-r8a77980" for R8A77980 (R-Car V3H) SCIF compatible UART.
     - "renesas,hscif-r8a77980" for R8A77980 (R-Car V3H) HSCIF compatible UART.
+    - "renesas,scif-r8a77990" for R8A77990 (R-Car E3) SCIF compatible UART.
+    - "renesas,hscif-r8a77990" for R8A77990 (R-Car E3) HSCIF compatible UART.
     - "renesas,scif-r8a77995" for R8A77995 (R-Car D3) SCIF compatible UART.
     - "renesas,hscif-r8a77995" for R8A77995 (R-Car D3) HSCIF compatible UART.
     - "renesas,scifa-sh73a0" for SH73A0 (SH-Mobile AG5) SCIFA compatible UART.