AMD encoding support

[vipotaenko02]

Not sure if this will work perfectly but I will continue to contribute to this request. I know support for AMD hardware encoding was dropped, but at least knowing the risk in edge cases like low-end CPU this may help. And there is also an opened issue about AMD pro drivers on Linux, which may help encoding work better there (not sure though, for now I can only test Windows support, but eventually I'll get working on a Linux support too). For the time being, while support is experimental I will build a forked version with changes I made there. If anyone's interested, testing will be greatly helpful.

[vipotaenko02]

For now the tasks are:

• Rewrite ffmpeg download while building, because for now it downloads a version without needed encoders
• Add encoder options, such as profile, etc
• Thoroughly test encoder support to not be worse then software one
• Make Linux support through the same encoders (if possible) or through vaapi

[Wieku]

@vipotaenko02 What's the status of this?

BTW The newest release of https://github.com/Wieku/FFmpeg-Builds should now support amf, can you test it?

[Wieku]

Except for import sorting it looks ok. I can merge it as soon as more granular control for qp is added (qp_i, qp_b, qp_p flags ig?)

[Wieku]

Please use gofmt instead of goimports for formatting. It looks better in general but for now I prefer to keep consistency.