[IA64-SGI] Add new vendor-specific SAL calls for:

- notifying the PROM of specific features that are supported by the OS.
  This is used to enable PROM feature if and only if the corresponding
  feature is implemented in the OS

- fetch feature sets that are supported by the current PROM. This allows
  the OS to selectively enable features when the PROM support is available.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>