ARM: tegra: jetson-tk1: mark eMMC as non-removable

The eMMC is soldered to the board, reflect this in the DT.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>