arm: tegra: add options for BOOTENV_EFI_SET_FDTFILE_FALLBACK for tegra186

Upstream linux DT naming doesn't align with the U-Boot DT, which may
not always be the case so this allows using BOOTENV_EFI_SET_FDTFILE_FALLBACK
where it might be appropriate for some boards.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>