Some x86 machines advertise the "hardware reduced" ACPI feature, advertise

Some x86 machines advertise the "hardware reduced" ACPI feature, advertise
S4 and S5 support, but fail to populate the SLEEP_CONTROL_REG and
SLEEP_STATUS_REG descriptions in the FADT.  An example of such a machine
is the ASUS Zenbook 14 UM433DA.  Any attempt to powerdown the machine
will result in a kernel crash.  It turns out that using the legacy ACPI PM
registers works fine on this machien.  So fall back on those registers
if SLEEP_CONTROL_REG and/or SLEEP_STATUS_REG aren't provided.

ok deraadt@, mpi@