vbo: Use _DrawVAO for array type draw commands.

vbo: Use _DrawVAO for array type draw commands.

Switch over to use the _DrawVAO for all the array type draws.
The _DrawVAO needs to be set before we enter _mesa_update_state, so move
setting the draw method in front of the first call to _mesa_update_state
which is in turn called from the *validate*Draw* calls. Using the
gl_vertex_array_object::_Enabled bitmask, gl_vertex_program_state::_VPMode
and gl_vertex_array_object::_AttributeMapMode we can already set
varying_vp_inputs before we call _mesa_update_state the first time.
Thus remove duplicate state validation.

v2: Update comments.

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