drm/virtio: use struct to pass params to virtio_gpu_object_create()

Create virtio_gpu_object_params, use that to pass object parameters to
virtio_gpu_object_create.  This is just the first step, followup patches
will add more parameters to the struct.  The plan is to use the struct
for all object parameters.

Drop unused "kernel" parameter for virtio_gpu_alloc_object(), it is
unused and always false.

Also drop "pinned" parameter.  virtio-gpu doesn't shuffle around
objects, so effecively they all are pinned anyway.  Hardcode
TTM_PL_FLAG_NO_EVICT so ttm knows.  Doesn't change much for the moment
as virtio-gpu supports TTM_PL_FLAG_TT only so there is no opportunity to
move around objects.  That'll probably change in the future though.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190318113332.10900-3-kraxel@redhat.com