tests: boards: neorv32: add build_all test for the NEORV32

Add a dedicated "build_all" test for the NEORV32 and its peripheral
drivers. These drivers depend on the NEORV32 SYSINFO (syscon) and thus
cannot easily be built for non-NEORV32 board targets.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>