[IA64] hotplug/ia64: SN Hotplug Driver - new SN PROM version code

This patch is a rewrite of the code to check the PROM version.  The current
code has some deficiences in the way PROM comparisons were made.  The minimum
value of PROM that will boot has also been changed to 4.04.

Signed-off-by: Prarit Bhargava <prarit@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>