ACPI / PM: Default to s2idle in all machines supporting LP S0

The Dell Venue Pro 7140 supports the Low Power S0 Idle state, but
does not support any of the _DSM functions that the current heuristic
checks for.

Since suspend-to-mem can not be safely performed on this machine,
and since the bitfield check can't cover this case, it is safer
to enable s2idle by default by checking for the presence of the
_DSM alone and removing the bitfield check.

Signed-off-by: Tristian Celestin <tristiancelestin@fastmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>