esp32/mpthreadport: Use binary semaphore instead of mutex.

So a lock can be acquired on one Python thread and then released on
another.  A test for this is added.

Signed-off-by: Damien George <damien@micropython.org>

tests/thread/thread_lock5.py

@@ -0,0 +1,16 @@
+# test _thread lock objects where a lock is acquired/released by a different thread
+
+import _thread
+
+
+def thread_entry():
+    print("thread about to release lock")
+    lock.release()
+
+
+lock = _thread.allocate_lock()
+lock.acquire()
+_thread.start_new_thread(thread_entry, ())
+lock.acquire()
+print("main has lock")
+lock.release()