QSV: add an option to force software decoding.
QSV: add an option to force software decoding.

Example use cases:

- convenient for testing during development

- using filters which haven't been validated (framerate shaping, decomb, etc.)

- improving memcpy speed when using old Intel drivers
Revert "QSV: add an option to force software decoding."

This reverts commit 02c532c57162c525bfd3592c055a43a10d85a48b.