riscv: Complete efi header for RV32/64

This patch depends on Atish's patch.
(https://patchwork.ozlabs.org/project/uboot/patch/20201013192331.3236458-1-atish.patra@wdc.com/)

Add fields to complete Optional Header "Data Directories" specified in the document.
(https://docs.microsoft.com/en-us/windows/win32/debug/pe-format

)

Signed-off-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Cc: rick@andestech.com
Cc: alankao@andestech.com
Cc: atish.patra@wdc.com
Cc: xypron.glpk@gmx.de
Cc: bmeng.cn@gmail.com
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Atish Patra <atish.patra@wdc.com>