grub2 is no fun on RISCV, as far as I can see. SiFive seem to prefer U-Boot.

If I understood the process right, a system is supposed to have a very 
small first stage that prepares a device tree with the mainboard 
resources that cannot be probed without special knowledge, that then 
loads OpenSBI, which provides a few generic boot services and emulation 
of missing instructions, and then another bootloader stage on top of 
that that can then load ELF or EFI kernels.

Bootloader internal handover is a device tree that is, for some 
inexplicable reason, flattened, and that needs to be converted to an 
ACPI tree (and flattened again, because that is how ACPI rolls) for EFI. 
Handover to an ELF kernel can just use the flat device tree directly, 
that's a little less silly.

    Simon