Use enum accessibility in types and member functions

Use enum accessibility in types and member functions

This changes nested types and member functions to use the new
'accessibility' enum, rather than separate private/protected flags.
This is done for consistency, but it also lets us simplify some other
code in the next patch.

Acked-By: Simon Marchi <simon.marchi@efficios.com>
Reviewed-by: Keith Seitz <keiths@redhat.com>