env: ti: android: boot with FIT Image

Boot android over emmc by default thru FIT image

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>