Qurt platform custom icm42688p IMU driver (#20753)

- first version of IMU driver for the VOXL 2 platform (Qurt)
 - this is a customized version of the Invensense ICM42688P driver, it is currently in the VOXL 2 board directory

platforms/qurt/src/px4/CMakeLists.txt

@@ -44,3 +44,4 @@ add_library(px4_layer
 )
 
 target_link_libraries(px4_layer PRIVATE work_queue)
+target_link_libraries(px4_layer PRIVATE drivers_board)

platforms/qurt/src/px4/tasks.cpp

@@ -66,6 +66,14 @@ static task_entry_t taskmap[PX4_MAX_TASKS];
 static bool task_mutex_initialized = false;
 static pthread_mutex_t task_mutex;
 
+// These are some Qurt pthread stubs needed for compilation and linking
+extern "C" {
+
+	int pthread_setname_np(pthread_t __target_thread, const char *__name) {	return 0; }
+	int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy) { return 0; }
+
+}
+
 static void *entry_adapter(void *ptr)
 {
 	task_entry_t *data;
@@ -147,11 +155,12 @@ static px4_task_t px4_task_spawn_internal(const char *name, int priority, px4_ma
 		return -1;
 	}
 
-	priority = 255 - priority;
-
-	if (priority < 5) { priority = 5; }
-
-	if (priority > 250) { priority = 250; }
+	// Qurt threads have different priority numbers. 1 is the highest
+	// priority and 254 is the lowest. But we are using the pthread
+	// implementation on Qurt which returns 255 when you call sched_get_priority_max.
+	// So, the big assumption is that the Qurt pthread implementation deals with
+	// this properly when creating the underlying Qurt task.
+	// TODO: Needs to be verified!
 
 	if (strlen(name) >= PX4_TASK_MAX_NAME_LENGTH) {
 		pthread_mutex_unlock(&task_mutex);