artik533s: update rootfs release meta information
artik533s: update rootfs release meta information

This patch updates the rootfs metadata to download the root file system
tarball from the github release site.

Change-Id: I2f8e5a73d0d311e0e719283e6ade6a992bfbd03a
Signed-off-by: Chanho Park <8ec285a53e21b773fd914e03c50e1b6431bc9aa8@samsung.com>

SamsungARTIK/build-artik