PM: suspend: Rename pm_suspend_via_s2idle()

The name of pm_suspend_via_s2idle() is confusing, as it doesn't
reflect the purpose of the function precisely enough and it is
very similar to pm_suspend_via_firmware(), which has a different
purpose, so rename it as pm_suspend_default_s2idle() and update
its only caller, i8042_register_ports(), accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>