dt-bindings: serial: renesas,scif: Document RZ/G2UL SoC

Add SCIF binding documentation for Renesas RZ/G2UL SoC. SCIF block on
RZ/G2UL is identical to one found on the RZ/G2L SoC. No driver changes
are required as RZ/G2L compatible string "renesas,scif-r9a07g044" will
be used as a fallback.

Whilst dropped the comments after RZ/G2{L,LC} fallback as to
avoid updating the comment over and over again when a new IP
is added

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20220207142213.19552-2-biju.das.jz@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>