Rework samples to use DEVICE_DT_GET and DT_CHOSEN
to get default display controller device.
Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>
This should align with subsys/display which we do not have yet. Plan is
to move lib/gui into subsys/display.
Signed-off-by: Anas Nashif <anas.nashif@intel.com>