boards: renesas: Create h3ulcb all-in-one doc

Merge both dedicated r7 and a57 h3ulcb boards doc
into an all-in-one documentation and take advantage
of these new boards documentation features:
- zephyr:board
- zephyr:board-supported-hw
- zephyr:board-supported-runners

Signed-off-by: Aymeric Aillet <aymeric.aillet@iot.bzh>
6 files changed