[IA64] SN2: Fix up sn2_rtc clock

[IA64] SN2: Fix up sn2_rtc clock

If the sn2_rtc clock is present then it is a must have since sn2_rtc
provides a synchronized time source on Altix systems. So elevate
the priority to 450. Otherwise the ITC would take precendence. Altix
systems currently do not boot because the ITC clocksource is broken. It
seems to assume that ITCs are synchronized and as a result nanosleep
hangs (may be fixed in a different patch).

While we are at it: Remove the sn2_mc definition. The sn2_rtc has a fixed
address. No point in reading the address from memory. Removing it avoids
touching one cacheline.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>