After reboot, it's not possible to use hotkeys to enter BIOS setup
and boot menu on some HP laptops.

BIOS folks identified the root cause is the missing _PTS call, and
BIOS is expecting _PTS to do proper reset.

Using S5 for reboot is default behavior under Windows, "A full
shutdown (S5) occurs when a system restart is requested" [1], so
let's do the same here.

[1] https://docs.microsoft.com/en-us/windows/win32/power/system-power-statesSigned-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>