drm/vmwgfx: Move screen object page flip to atomic function

The dmabuf_dirty/surface_dirty in case of screen object is moved to
plane atomic update, so that page flip in atomic ioctl also works.

vmwgfx does not support DRM_MODE_PAGE_FLIP_ASYNC, so this flag is never
expected.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>