IO: Add lazy atomic OR, AND and CLEAR functions for flags

IO needs atomic updates of a few critical status flags, but doing these always atomic (with interrupts disabled) might cause a too high interrupts disabled interval. In order to avoid this only operations that change the state of the target variable are done with interrupts disabled, while operations without an effect on the target variable are not executed.

src/modules/px4iofirmware/safety.c

@@ -117,7 +117,7 @@ safety_check_button(void *arg)
 
 		} else if (counter == ARM_COUNTER_THRESHOLD) {
 			/* switch to armed state */
-			PX4_CRITICAL_SECTION(r_status_flags |= PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
+			PX4_ATOMIC_MODIFY_OR(r_status_flags, PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
 			counter++;
 		}
 
@@ -128,7 +128,7 @@ safety_check_button(void *arg)
 
 		} else if (counter == ARM_COUNTER_THRESHOLD) {
 			/* change to disarmed state and notify the FMU */
-			PX4_CRITICAL_SECTION(r_status_flags &= ~PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
+			PX4_ATOMIC_MODIFY_CLEAR(r_status_flags, PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
 			counter++;
 		}