esp32: Adds gcov over JTAG feature

Implements function to dump GCOV data to host via JTAG.
The following functionality was added:
 - Host file I/O
 - GCOV runtime I/O stubs
 - GCOV example

examples/system/gcov/main/gcov_example_func.c

@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+
+void blink_dummy_func(void)
+{
+    static int i;
+    printf("Counter = %d\n", i++);
+}
+