Set a GPT label for EFI partition

[ocochard]

This allow to easly update the EFI loader and sync with a standard FreeBSD install.

[evadot]

We probably should use the same name as the installer and iirc we don't use "efiboot0" there.

[bsdimp]

I believe we're standardizing on efiboot0 everywhere.
IIRC old versions of bsdinstall used efiboot, but when multi-esp support was added, it was added as efiboot%d starting at 0.

[evadot]

I believe we're standardizing on efiboot0 everywhere. IIRC old versions of bsdinstall used efiboot, but when multi-esp support was added, it was added as efiboot%d starting at 0.

Yes indeed.