QSV: move QSV-specific common code to decicated files.
QSV: decavcodec, code simplification and cleanup.
QSV: use software decoding for 10-bit H.264 sources.
QSV: simplify a check.
QSV: cleanup filter initialization.

The UIs are now only responsible for adding the software filters, whereas libhb is
reponsible for replacing them with hardware-accelerated variants when applicable.
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