can: rcar_canfd: Add suspend/resume support

can: rcar_canfd: Add suspend/resume support

On R-Car Gen3 using PSCI, s2ram powers down the SoC.  After resume, the
CAN-FD interface no longer works.  Trying to bring it up again fails:

    # ip link set can0 up
    RTNETLINK answers: Connection timed out

    # dmesg
    ...
    channel 0 communication state failed

Fix this by populating the (currently empty) suspend and resume
callbacks, to stop/start the individual CAN-FD channels, and
(de)initialize the CAN-FD controller.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://patch.msgid.link/20251124102837.106973-8-biju.das.jz@bp.renesas.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>