[IA64] Updates to the sn2_defconfig for 2.6.15.

This updates the sn2_defconfig file for the Altix 330 hardware, enables
the AGP graphics for the SGI Prism, and removes prompts for the remainder
of the new features.  Greg Edwards reviewed the changes.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Greg Edwards <edwardsg@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>