samples: boards: nordic: coresight_stm: Improve benchmark

Add interrupt locking during test to ensure that main thread is not
interrupts which would impact the test.

Add longer sleep time between tests to ensure that all logs are
processed on time and not dropped.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

samples/boards/nordic/coresight_stm/src/main.c

@@ -16,12 +16,14 @@ LOG_MODULE_REGISTER(app);
 
 #define TEST_LOG(rpt, item)                                                                        \
 	({                                                                                         \
+		uint32_t key = irq_lock();                                                         \
 		uint32_t t = k_cycle_get_32();                                                     \
 		for (uint32_t i = 0; i < rpt; i++) {                                               \
 			__DEBRACKET item;                                                          \
 		}                                                                                  \
 		t = k_cycle_get_32() - t;                                                          \
-		k_msleep(200);                                                                     \
+		irq_unlock(key);                                                                   \
+		k_msleep(400);                                                                     \
 		t;                                                                                 \
 	})