dfu: odroid xu3: Define DFU_MANIFEST_POLL_TIMEOUT to handle large files transmission and storage

As tested on the Odroid XU3, large files to be stored on the file system
require considerable time to be physically written to the medium.

The default 300 ms is not enough to store large file (e.g. 26 MiB).
To fix this situation the DFU_MANIFEST_POLL_TIMEOUT has been defined.

It is used to cease the communication with dfu-util and allow the target
board to store the data on file system.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>