can: rcar_canfd: Enhance multi_channel_irqs handling

Currently multi_channel_irqs has only 2 channels. But RZ/G3E has six
channels. Enhance multi_channel_irqs handling to support more than two
channels.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://patch.msgid.link/20250417054320.14100-19-biju.das.jz@bp.renesas.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>