mesa: Use VERT_ATTRIB_* indexed array in gl_array_object.

mesa: Use VERT_ATTRIB_* indexed array in gl_array_object.

Replace the distinct struct gl_client_array members in gl_array_object by
an array of gl_client_arrays indexed by VERT_ATTRIB_*.
Renumber the vertex attributes slightly to keep the old semantics of the
distinct array members. Make use of the upper 32 bits in VERT_BIT_*.
Update all occurances of the distinct struct members with the array
equivalents.

Signed-off-by: Mathias Froehlich <Mathias.Froehlich@web.de>
Reviewed-by: Eric Anholt <eric@anholt.net>