boards: stm32: Add zephyr_udc0 to nucleo_h503rb

[wjklimek1]

Added config of USB peripheral for Nucleo H503RB. Examples using USB now compile and work correctly.

When I tried to run USB examples for this board turned out that USB pins are not defined in .dts file. After adding configuration I was able to successfully compile and run code from examples.

[github-actions]

Hello @wjklimek1, and thank you very much for your first pull request to the Zephyr project!
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[erwango]

LGTM, but please add usb_device in supported field of board .yaml file

[github-actions]

Hi @wjklimek1!
Congratulations on getting your very first Zephyr pull request merged 🎉🥳. This is a fantastic achievement, and we're thrilled to have you as part of our community!

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Thank you for your valuable input, and we look forward to seeing more of your contributions in the future! 🪁