EMC voltage for Mariko; Fix #60; Show battery & voltage info in overlay on Erista

- From previous analysis, EMC voltage is set before AMS loads on Mariko, and will not be set again or changed afterwards.

- sys-clk-OC will take care of setting emc voltage on Mariko once it loads.

- OS will not hang at boot as it always boots with EMC @ 1600 MHz.

Source/sys-clk-OC/common/include/cpp_util.hpp

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <utility>
+
+template<typename F>
+class ScopeGuard {
+public:
+    ScopeGuard(F&& f)
+     : f(f), engaged(true) {};
+
+    ~ScopeGuard() {
+        if (engaged)
+            f();
+    };
+
+    ScopeGuard(ScopeGuard&& rhs)
+     : f(std::move(rhs.f)) {};
+
+    void dismiss() { engaged = false; }
+
+private:
+    F f;
+    bool engaged;
+};
+
+struct MakeScopeExit {
+    template<typename F>
+    ScopeGuard<F> operator+=(F&& f) {
+        return ScopeGuard<F>(std::move(f));
+    };
+};
+
+#define STRING_CAT2(x, y) x##y
+#define STRING_CAT(x, y) STRING_CAT2(x, y)
+#define SCOPE_GUARD MakeScopeExit() += [&]() __attribute__((always_inline))
+#define SCOPE_EXIT auto STRING_CAT(scope_exit_, __LINE__) = SCOPE_GUARD