RISC-V: Align boot image header with Linux

RISC-V: Align boot image header with Linux

The released Linux boot image header in v5.3 is different from the
one present in U-Boot. Align the header with the new version. The
changes in Linux are backward compatible. Previous U-Boot releases
with older header will continue to work as well. As v5.3 kernel is
the first one to support image header, there is no compatibility
issue between new U-Boot (with this patch) and older kernel.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Rick Chen <rick@andestech.com>