[U-Boot] [ANN] U-Boot v2019.04-rc3 released

Hey all,

So it's release day and I've put up v2019.04-rc3, I've updated git and the tarballs are also up now.

Thanks again to having signed tags, between -rc2 and -rc3 we have a good changelog under 'git log --merges v2019.04-rc2..v2019.04-rc3'

We're looking at release on April 8th, 2019.

Thanks all!