dxva2: compatibility with mingw-w64 trunk

Includes initguid.h and use existing DEFINE_GUID
Add MS_GUID for GUIDs that should be declared only if missing from dxva2api.h
(really, those should move to videolan's dxva2api.h)
Move DXVA_NoEncrypt away from codec GUIDs
Sort the GUIDs by codec, align properly