This commit uses the new .. zephyr:code-sample-category directive to
categorize code samples across the tree.
Updates existing legacy references to manually defined targets to now
use :zephyr:code-sample-category: role instead.
Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>
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>