Move get ipmi id into the match function.  This prevents attach from being called whenever there is no BMC and hence suppresses a ugly message when a bios lied that it had ipmi.
Move get ipmi id into the match function.  This prevents attach from being
called whenever there is no BMC and hence suppresses a ugly message when a
bios lied that it had ipmi.

tested beck@

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