D3D12: Implement XFB encoding/decoding (support Real XFB)

Source/Core/VideoBackends/D3D12/D3DUtil.h

@@ -22,7 +22,11 @@ extern StateCache gx_state_cache;
 namespace D3D
 {
 
-unsigned int AlignValue(unsigned int value, unsigned int alignment);
+constexpr unsigned int AlignValue(unsigned int value, unsigned int alignment)
+{
+	return (value + (alignment - 1)) & ~(alignment - 1);
+}
+
 void ResourceBarrier(ID3D12GraphicsCommandList* command_list, ID3D12Resource* resource, D3D12_RESOURCE_STATES state_before, D3D12_RESOURCE_STATES state_after, UINT subresource);
 
 // Font creation flags