i965: Implement the GL_ARB_base_instance extension.

i965: Implement the GL_ARB_base_instance extension.

Thanks to Fredrik Höglund, all the hard work was already done.

Tested using a modified oglconform (that actually runs these tests on
our driver); it looks like there may be some bugs when using client
arrays.  All applicable non-compatibility tests passed.

For now, only enable it in core profiles.

Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Ian Romanick <idr@freedesktop.org>