virtual_oss: Add SPDX-License-Identifier tags

[tuukka.pasanen_ilmi.fi]

Summary

These files has correct BSD-2-Clause license text but in some files there is dedication text inside license area:

*              This software is dedicated to the memory of -
*         Baron James Anlezark (Barry) - 1 Jan 1949 - 13 May 2012.
*
*              Barry was a man who loved his music.

Text probably does not affect SPDX-License-Identifier-tag but it's not copyright of anything but some additional text in license section.

Sponsored by: The FreeBSD Foundation