imxrt-multi: CM4_RUN_CORE returns EALREADY if core is running

Useful when we need to run new code on an already running M4 core.
The error code EALREADY allows us to detect this situation, in which
case the new code should be started by resetting the M4 core.

DONE: NIL-441

multi/imxrt-multi/cm4.c

@@ -366,6 +366,11 @@ static int runCore(unsigned int offset)
 	platformctl_t pctl;
 	unsigned int vectors = (unsigned int)CM4_MEMORY_START + offset;
 
+	if ((*(m4_common.src + src_scr) & 1) != 0) {
+		/* Core is already running */
+		return -EALREADY;
+	}
+
 	/* Set CM4's VTOR to the start of it's memory */
 	pctl.action = pctl_set;
 	pctl.type = pctl_iolpsrgpr;