zephyr: sync: Add Mutex::new and Condvar::new

Add dynamic allocation support to the sync Mutex and Condvar.  When
allocation is available, and userspace is not used, these can be used
pretty much the same as those from std.

Signed-off-by: David Brown <david.brown@linaro.org>

Author: d3zd3z

zephyr/src/sync.rs

@@ -119,6 +119,12 @@ impl<T> Mutex<T> {
     pub const fn new_from(t: T, raw_mutex: sys::Mutex) -> Mutex<T> {
         Mutex { inner: raw_mutex, data: UnsafeCell::new(t) }
     }
+
+    /// Construct a new Mutex, dynamically allocating the underlying sys Mutex.
+    #[cfg(CONFIG_RUST_ALLOC)]
+    pub fn new(t: T) -> Mutex<T> {
+        Mutex::new_from(t, sys::Mutex::new().unwrap())
+    }
 }
 
 impl<T: ?Sized> Mutex<T> {
@@ -216,6 +222,12 @@ impl Condvar {
         Condvar { inner: raw_condvar }
     }
 
+    /// Construct a new Condvar, dynamically allocating the underlying Zephyr `k_condvar`.
+    #[cfg(CONFIG_RUST_ALLOC)]
+    pub fn new() -> Condvar {
+        Condvar::new_from(sys::Condvar::new().unwrap())
+    }
+
     /// Blocks the current thread until this conditional variable receives a notification.
     ///
     /// This function will automatically unlock the mutex specified (represented by `guard`) and