contrib: libplacebo: update to 5.264.1

We need to force the path to find SPIRV otherwise find_library() doesn't find it even though it's in the contrib (from glslang). find_library() doesn't use the libdir we pass when configuring the code. It seems more designed to find system libraries. But it's possible to add custom pathes to find more libraries. This is what the added patch does.

With this fix we should also be able to enable the D3D11 output in libplacebo.