board:samsung:trats/trats2: enable boot with appended and separated DTB

board:samsung:trats/trats2: enable boot with appended and separated DTB

This patch modifies envs to enable dual kernel boot
 - with separated DTB if the DTB file is loaded successfully;
 - with DTB apppended to uImage if DTB file is not found;
This is neccesssary for backward compatibilty.

Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>