mx6slevk: Use PARTUUID to specify the rootfs location
mx6slevk can run different kernel versions, such as NXP 4.1 or mainline.
Currently the rootfs location is passed via mmcblk number and the
problem with this approach is that the mmcblk number for the SD
card changes depending on the kernel version.
In order to avoid such issue, use the UUID method to specify the
rootfs location.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
(cherry picked from commit
a0046393dae74364b7a7b7ed5e2af8431a3d680c)
