Unable to get Intel HD 4000 graphics and audio working on EFI install of Windows 10 Bootcamp on Macbook Pro mid 2012
I realize this is an old thread, but I had this same issue and I was finally able to get the on board audio working by following this:

https://egpu.io/forums/pc-setup/fix-dsdt-override-to-correct-error-12/

I think they attempted this in order to install an eGPU but it serves the purpose of allowing the on-board audio to work. The only thing that isn't working on my 2012 non-retina MBP is the on board graphics driver (Intel Graphics HD 4000) which is fine because the NVIDIA drivers work fine (only with the most recent driver patch from December 28, 2018, the "current" drivers from December 12 crash the computer) and allow proper "sleep" which wasn't possible previously. 

Only feature that doesn't work is the ability to adjust the brightness. Staring at this very bright screen will drive me crazy, but in trying to fix this one last problem, I have had to re-install Windows twice, so I am about ready to give up. Any ideas?