Merge https://gitlab.denx.de/u-boot/custodians/u-boot-riscv

- Fix HiFive Unleashed the broken problem by call fix_fdt() before
  reserve_fdt().  Please refer to
  https://www.mail-archive.com/[email protected]/msg379444.html for
  master u-boot broken for HiFive Unleashed.
- Add unaligned exception cmd.
- Refine sifive/fu540 spl flow.
- Add  additional crash information for efi.
- Update sipeed/maix doc.
- Two minor refine.