Ignore buttons for which _STA indicates they're not present, enabled or functioning.  Fixes suspend/resume on a Dell PowerEdge T20.
Ignore buttons for which _STA indicates they're not present, enabled or
functioning.  Fixes suspend/resume on a Dell PowerEdge T20.

ok mlarkin@, sthen@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars