Alexander Schrijver posted a diff to remove references to the c_rehash script,
which we don;t have in base. after some discussion with jca, i've not removed
these references, but tried to make it clearer it's distributed with openssl
and not included in base;
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@