accidentally enable non-existent states.
This bug was triggered if ACPI advertises the presence of a C2 state
which we fail to parse via acpi_PkgGas due to our lack of support for
FFixedHW resources, and causes an immediate panic when an attempt is
made to enter the (NULL) state.
One affected platform is the EC2 c4.8xlarge VM instance type; there
may be others.
MFC after: 1 week
Thanks to: jkim, @_msw_
633a28478c