mesa/vbo: add support for 64-bit vertex attributes. (v1)

mesa/vbo: add support for 64-bit vertex attributes. (v1)

This adds support in the vbo and array code to handle
double vertex attributes.

v0.2: merge code to handle doubles in vbo layer.
v1: don't use v0, merge api_array elt code.

Acked-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>