dt-bindings: serial: Add documentation for Renesas RZ/V2H(P) (R9A09G057) SCIF support

Document support for the Serial Communication Interface with FIFO (SCIF)
available in the Renesas RZ/V2H(P) (R9A09G057) SoC. The SCIF interface in
the Renesas RZ/V2H(P) is similar to that available in the RZ/G2L
(R9A07G044) SoC, with the following differences:

- RZ/V2H(P) SoC has three additional interrupts: one for Tx end/Rx ready
and two for Rx and Tx buffer full, all of which are edge-triggered.
- RZ/V2H(P) supports asynchronous mode, whereas RZ/G2L supports both
synchronous and asynchronous modes.
- There are differences in the configuration of certain registers such
as SCSMR, SCFCR, and SCSPTR between the two SoCs.

To handle these differences in the driver, a new SoC-specific compatible
string is added, ensuring proper handling of the unique features and
register configurations of the RZ/V2H(P) SoC.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20240604170513.522631-5-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>