Split uImage on "clean" uImage and Device Tree blob.

Split uImage on "clean" uImage and Device Tree blob.

1. The change is due to upgrade u-boot to latest upstream version
   which support separate uImage and DTB.
   Addtionally current defult u-boot configuration for trats2 assumes
   that kernel image and DTB are delivered as separat files.

2. DTB files are located in /boot directory.

3. Together with uImage are delivered all DTBs which are compatible with
   tizen_defconfig kernel configuration.

Change-Id: I60a581edb4edccbf2ef704de525409da6572c4f8
Signed-off-by: Jacek Pielaszkiewicz <j.pielaszkie@samsung.com>