mediafoundation: Fix for UWP build
We don't support D3D11 interop for UWP because some APIs (specifically MFTEnum2) are desktop application only. However, the code for symbol loading is commonly used by both UWP and WIN32. Just link GModule unconditionally which is UWP compatible, and simply don't try to load any library/symbol dynamically when D3D11 interop is unavailable.