Add support for qom types provided by modules.  For starters use a
manually maintained list which maps qom type to module and prefix.

Two load functions are added:  One to load the module for a specific
type, and one to load all modules (needed for object/device lists as
printed by -- for example -- qemu -device help).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20200624131045.14512-2-kraxel@redhat.com