[Task]: Move Radxa 5B+ and 5T (Platinum) to Mainline U-Boot

[HeyMeco]

Task description

To-Do

• Radxa Rock 5B+
• Radxa Rock 5T

Benefit: More robust, up to date & no downsides.

For implementation / patch reference: https://gitlab.collabora.com/hardware-enablement/rockchip-3588/u-boot

[github-actions]

Jira ticket: AR-2780