[U-Boot] riscv: Add support for HI20 PE relocations

[Alexander Graf]

> The PE standard allows for HI20/LOW12 relocations. Within the efi_loader
> target we always know that our relocation target is 4k aligned, so we
> don't need to worry about the LOW12 part.
> 
> This patch adds support for the respective relocations. With this and a
> few grub patches I have cooking in parallel I'm able to run grub on RISC-V.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>

Thanks, applied to efi-next

Alex