QNX: Restructure plugins

Now that the MmRenderer implementation is ported to plain QNX, rename
the directories and files accordingly:

"blackberry" becomes "qnx", replace the Bb prefix with MmRenderer for
classes concerned with mm-renderer. The legacy alsa support for plain qnx
is now "qnx-audio".

Change-Id: I6abd98ecdd713b2d5e554d42224dc30f13772f43
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>