samples: watchdog: board s32z270dc2_r52 only build and not running

 Currently, the s32z270dc2_r52 board only supports running on RAM,
 so samples or tests watchdogs that perform SoC reset will not produce
 results. Set the build only for these samples and tests until the
 reset SoC function is supported.

Signed-off-by: Quang Bui Trong <quang.buitrong@nxp.com>