Lockscreen: check for 600dp device to hide minimize challenge option

Change-Id: Ie2d281cdf22d16ba4d63ad5b81f1a1ad18e5617c
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Merge "Lockscreen: check for 600dp device to hide minimize challenge option" into jb-mr1