Use the OTP DM driver to set the serial environment variable. Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Tested-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Jagan Teki <jagan@amarulasolutions.com> Tested-by: Jagan Teki <jagan@amarulasolutions.com>