[IA64] IOC4 config option ordering

SERIAL_SGI_IOC4 and BLK_DEV_SGIIOC4 depend upon SGI_IOC4, and
SERIAL_SGI_IOC3 depends upon SGI_IOC3.  Currently the definitions
are out of order in the config sequence.

Fix by including drivers/sn/Kconfig immediately after SGI_SN,
upon which SGI_IOC4 and SGI_IOC3 depend.

Signed-off-by: Brent Casavant <bcasavan@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>