mesa: add _NEW_VARYING_VP_INPUTS for gl_context::varying_vp_inputs

mesa: add _NEW_VARYING_VP_INPUTS for gl_context::varying_vp_inputs

This is a frequently-updated state and _NEW_ARRAY already causes revalidation
of the vbo module. It's kinda counter-productive to recompute arrays
in the vbo module if _NEW_ARRAY is set and then set _NEW_ARRAY again.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Mathias Fröhlich <Mathias.Froehlich@web.de>