arm64: dts: renesas: r8a779a0: Add family fallback for CSISP IP

arm64: dts: renesas: r8a779a0: Add family fallback for CSISP IP

To make it easier to support new R-Car Gen4 SoCs add a family fallback
compatible similar to what was done for VIN on R-Car Gen4.

There is no functional change, but the addition of the family fallback
in the bindings produces warnings for R-Car V3U for DTS checks if they
are not added.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20240826144352.3026980-4-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>