[IA64] show "SN Devices" menu only if CONFIG_SGI_SN

Adrian> On architectures like i386, the "Multimedia Capabilities Port
Adrian> drivers" menu is visible, but it can't be visited since it
Adrian> contains nothing usable for CONFIG_SGI_SN=n.

Jes> Thats only a third of the patch, if you want to do that, you should
Jes> remove the redundant SGI_SN checks below.

Signed-off-by: Tony Luck <tony.luck@intel.com>