dt-bindings: serial: renesas,rsci: Document RZ/G3E support

dt-bindings: serial: renesas,rsci: Document RZ/G3E support

Add documentation for the serial communication interface (RSCI) found on
the Renesas RZ/G3E (R9A09G047) SoC. The RSCI IP on this SoC is identical
to that on the RZ/T2H (R9A09G077) SoC, but it has a 32-stage FIFO compared
to 16 on RZ/T2H. It supports both FIFO and non-FIFO mode operation. RZ/G3E
has 6 clocks(5 module clocks + 1 external clock) compared to 3 clocks
(2 module clocks + 1 external clock) on RZ/T2H, and it has multiple resets.
It has 6 interrupts compared to 4 on RZ/T2H.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/20251129164325.209213-2-biju.das.jz@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>