[ANN] U-Boot v2021.04-rc1 released

Hey all,

It's release day, and here's v2021.04-rc1. As is often the case, there's a few PRs still I would have hoped to see by now come in but I think will be coming in soon. And there's a few more changes in my own queue that I think I can / should pick up still and I'll try and get to this week. As always, I leave what comes in at this point to the discretion of the custodians making the PRs.

In terms of a changelog, git log --merges v2021.01..v2021.04-rc1 contains what I've pulled but as always, better PR messages and tags will provide better results here.

I do have my reminders setup for doing -rc releases every other Monday from here on out and final release on April 5th, 2021. Thanks all!