[IA64] Ski simulator doesn't need check_sal_cache_flush

Peter Chubb reported that commit 3463a93d


(Update check_sal_cache_flush to use platform_send_ipi()) broke
Ski because it does not implement IPIs.

Tony Luck suggested we just #ifndef out the call (since the simulator
does not have the SAL bug that this code is attempting to detect and
workaround)

Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>