text: add owner field to text-ops

When text-ops are registered via modules, we need an owner field so
they're correctly tracked. Hence, add this field to all text-ops and
correctly keep module references.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
kmscon: move bbulk renderer into module

Provide the bbulk renderer via mod-bbulk.so so it can be loaded during
runtime.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
kmscon: move gltex renderer into module

Provide the gltex renderer via a module to allow loading it during
runtime.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
build: remove libfont.la and link directly

We no longer share libfont.la so link it directly into kmscon.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
kmscon: make bblit mandatory

Similar to the font backends we now require one backend to be always
available as safe fallback. The bblit backend is the most basic backend so
make it mandatory and link it unconditionally.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
text: remove old init/deinit helpers

We no longer need these helpers so remove them. We require each backend to
register itself as part of module-loading so no need to keep these
helpers.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>