drm/virtio: fix resource id handling

Move virtio_gpu_resource_id_{get,put} to virtgpu_object.c and make them
static.  Allocate and free the id on creation and destroy, drop all
other calls.  That way objects have a valid handle for the whole
lifetime of the object.

Also fixes ids leaking.  Worst offender are dumb buffers, and I think
some error paths too.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20181019061847.18958-7-kraxel@redhat.com