spice: fix broken initialization

Commit 1b71f7c14fab6f00c2680d4489fbee7baf796e4f moved MODULE_INIT_QOM to
way before MODULE_INIT_MACHINE, thereby breaking assumptions made in
spice-core.c which registered both a type initializer and a machine
intializer.

This fix removes the type registration, and replaces it with calling
qemu_spice_init in vl.c after command line parsing (second pass) is
done, and after timers are armed, required by spice server.

Signed-off-by: Alon Levy <alevy@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
