If the Embedded Contoller device has a _STA method, evaluate it and bail out early during attach if it signals that the device isn't present.
If the Embedded Contoller device has a _STA method, evaluate it and bail out
early during attach if it signals that the device isn't present.

Reduces the noise on machines where the AML provides an (incomplete)
description of the Embedded Controller but doesn't actually have one.

ok mlarkin@, deraadt@

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