drm/vmwgfx: Split surface metadata from struct vmw_surface

Create a new structure vmw_surface_metadata representing the metadata
used for creating surface. With this can make the surface_define_priv
a bit cleaner.

Signed-off-by: Deepak Rawat <drawat.floss@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Thomas Hellström (VMware) <thomas_os@shipmail.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Signed-off-by: Roland Scheidegger <sroland@vmware.com>