Apply constexpr on global constant varaibles

When HIP_ENABLE_DEFERRED_LOADING=0, many global variables will be
referenced but they are not initialized in that early time. The patch
will use constexpr to initialze global constant varables in compile
time.

Change-Id: I9d538b7abc6a0ce700ec3332b97fc144db5fc1ef

rocclr/platform/commandqueue.hpp

@@ -46,7 +46,7 @@ class DeviceQueue;
 
 class CommandQueue : public RuntimeObject {
  public:
-  static const uint RealTimeDisabled = 0xffffffff;
+  static constexpr uint RealTimeDisabled = 0xffffffff;
   enum class Priority : uint { Low = 0, Normal , Medium, High };
 
   struct Properties {