[v2] include: unexport symbols from opaque.h

several symbols in opaque.h aren't used by any drivers or modules, thus don't need to exported.

checked against internal .so's as well as all driver trees at gitlab (as well as tigervnc).

tigervnc does use some of those symbols, but only in their DDX, thus compiled-in and not relying on exporting.

Changes v2:

• some more refinements on commit messages
• resolved conflicts