SpdConstants and SpdLinearSamplerConstants

[sagaceilo]

I think it would be better to move

        struct SpdConstants
        {
            int mips;
            int numWorkGroupsPerSlice;
            int workGroupOffset[2];
        };

        struct SpdLinearSamplerConstants
        {
            int mips;
            int numWorkGroupsPerSlice;
            int workGroupOffset[2];
            float invInputSize[2];
            float padding[2];
        };

To ffx_spd.h under a A_CPU define. That would make it more convinient of using just

#define A_CPU
#include <fidelityfx/ffx_a.h>
#include <fidelityfx/ffx_spd.h>

In the implementation file. Currently they are hidden in example project file.