Adds SHA256 Cryptocell code to bootloader (#432)

* adds bootloader code

* fix header and typos

bootloader/src/static_ref.rs

@@ -0,0 +1,46 @@
+//! Wrapper type for safe pointers to static memory.
+//!
+//! Imported from:
+//! https://github.com/tock/tock/blob/master/kernel/src/utilities/static_ref.rs
+
+use core::ops::Deref;
+
+/// A pointer to statically allocated mutable data such as memory mapped I/O
+/// registers.
+///
+/// This is a simple wrapper around a raw pointer that encapsulates an unsafe
+/// dereference in a safe manner. It serve the role of creating a `&'static T`
+/// given a raw address and acts similarly to `extern` definitions, except
+/// `StaticRef` is subject to module and crate boundaries, while `extern`
+/// definitions can be imported anywhere.
+#[derive(Debug)]
+pub struct StaticRef<T> {
+    ptr: *const T,
+}
+
+impl<T> StaticRef<T> {
+    /// Create a new `StaticRef` from a raw pointer
+    ///
+    /// ## Safety
+    ///
+    /// Callers must pass in a reference to statically allocated memory which
+    /// does not overlap with other values.
+    pub const unsafe fn new(ptr: *const T) -> StaticRef<T> {
+        StaticRef { ptr }
+    }
+}
+
+impl<T> Clone for StaticRef<T> {
+    fn clone(&self) -> Self {
+        StaticRef { ptr: self.ptr }
+    }
+}
+
+impl<T> Copy for StaticRef<T> {}
+
+impl<T> Deref for StaticRef<T> {
+    type Target = T;
+    fn deref(&self) -> &'static T {
+        unsafe { &*self.ptr }
+    }
+}