[IA64] fix ia64 Kconfig to allow CONFIG_PM on sn2

This probably should have been fixed when I fixed up the generic build for
discontig+numa machines, but oh well.

CONFIG_PM is allowable for generic builds but not for sn2 builds, which
doesn't make much sense, and in fact breaks the build if recent ACPI bits are
added to the tree.  It looks like the only arch that needs to prevent
CONFIG_PM stuff is the ski simulator (though those options could probably use
some cleanup as well), so remove the big conditional and replace it with a
simple test for IA64_HP_SIM instead.
Signed-off-by: Jesse Barnes <jbarnes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>