etc/mtree: Add package tags for /usr/include
Set the default package to clibs-dev, since that's where the vast
majority of include files comes from. Add explicit package tags
for the directories which are installed in their own package.
MFC after: 1 day
Reviewed by: emaste
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D53577