bdinfo: riscv: Use generic bd_info

bdinfo: riscv: Use generic bd_info

At present riscv still uses its own private bd_info struct. Move it over
to use the generic one like other archs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>