configs: TI: Enable FIT Library overlay support

Enable the FDT library overlay support for all TI SOC family.

Without this option, when Loading fdt from FIT image, the
following warning is seen.

"config with overlays but CONFIG_OF_LIBFDT_OVERLAY not set".

Signed-off-by: Praneeth Bajjuri <praneeth@ti.com>
Suggested-by: Andrew F.Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>