can: rcar_canfd: Add r8a7796 support

- compatible: Must contain one or more of the following:

  - "renesas,rcar-gen3-canfd" for R-Car Gen3 compatible controller.

  - "renesas,r8a7795-canfd" for R8A7795 (R-Car H3) compatible controller.

  - "renesas,r8a7796-canfd" for R8A7796 (R-Car M3) compatible controller.

  When compatible with the generic version, nodes must list the

  SoC-specific version corresponding to the platform first, followed by the

child node supports the "status" property only, which is used to

enable/disable the respective channel.

Required properties for "renesas,r8a7795-canfd" compatible:

In R8A7795 SoC, canfd clock is a div6 clock and can be used by both CAN

and CAN FD controller at the same time. It needs to be scaled to maximum

frequency if any of these controllers use it. This is done using the

below properties.

Required properties for "renesas,r8a7795-canfd" and "renesas,r8a7796-canfd"

compatible:

In R8A7795 and R8A7796 SoCs, canfd clock is a div6 clock and can be used by both

CAN and CAN FD controller at the same time. It needs to be scaled to maximum

frequency if any of these controllers use it. This is done using the below

properties:

- assigned-clocks: phandle of canfd clock.

- assigned-clock-rates: maximum frequency of this clock.