[IA64] Do not call SN_SAL_SET_CPU_NUMBER twice on cpu 0

This is an SN specific patch.

Architectually, cpu_init is always called twice on cpu 0
and thus resulted in two SN_SAL_SET_CPU_NUMBER calls.

This was harmless in production kernel; however, it can
cause problem on booting up a crashdump kernel at Altix.

Here is the patch that detects the second sn_cpu_init
call and skips the second call to SN_SAL_SET_CPU_NUMBER.

Signed-Off-By: Jay Lan <jlan@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>