boards: renesas: Enable CEU video capture support on EK-RA8D1

- Add CEU pin configuration to ek_ra8d1-pinctrl.dtsi
- Enable CEU node and Arducam 20-pin connector in ek_ra8d1.dts
- Configure PWM3 as external XCLK via pwm-clock node
- Update board YAML to declare video support

Signed-off-by: Duy Vo <duy.vo.xc@bp.renesas.com>
Signed-off-by: Khanh Nguyen <khanh.nguyen.wz@bp.renesas.com>