These tablets' DSDT does not set acpi_gbl_reduced_hardware, so
acpi_power_off gets used as pm_power_off handler. Not setting
acpi_gbl_reduced_hardware may very well be correct for these tablets,
but acpi_power_off is broken on them.

Using acpi_power_off causes "poweroff" to hang hard. Requiring pressing
the powerbutton for 30 seconds *twice* followed by a normal 3 second
press to recover.

Avoid this by overriding the global pm_power_off handler to do
an EFI poweroff, which does work, instead.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20220223133153.730337-5-hdegoede@redhat.com