Adds missing code-sample directive to all the NXP samples in
preparation for upcoming changes to the Zephyr documentation that will
be leveraging the provided description and metadata.
Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>
Group all NXP board samples in samples/boards/nxp to
keep samples/boards/ organized by vendor
Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>