Rob Clark has an RFC patch to U-Boot, with UEFI variable support:

[RFC] efi: variable support

Mapping from EFI variables to grub variables. Still almost as many TODOs as lines of code, but just figured I’d send out an early version for comments. I was thinking of it as a useful way for u-boot to pass values to grub (although grub is still missing a way for grub scripts to retrieve UEFI variables). The rough idea is to encode GUID + variable name plus “efi_” prefix (to avoid unintended u-boot variables leaking into the UEFI world). And then encode the type (and attributes?) in the string value of the variable. Ie. something like:

setenv efi_8be4df6193ca11d2aa0d00e098032b8c_OsIndicationsSupported (u64)0

Full patch/thread:
https://lists.denx.de/listinfo/u-boot