After discussions, revert svn r253708.

Changelog for 253708 was completely wrong and the code implemented something
non-standard for the wrong reasons.

Sponsored by:	Yahoo! Inc.
empirical testing showed that 3 seconds is just too slow for GET_DEVICE_ID
to return on newer Dell hardware.  Bump to 6 second timeouts until someone
has a better idea on how to handle this

Reviewed by:	jhb@
MFC after:	2 weeks
Sponsored by:	Yahoo! Inc.
Check for ipmi_attached in ipmi_isa_probe as a suggested alternative to
ipmi_isa_attach.  This keeps unintended but harmless noise about "ipmi1"
from appearing in the boot up sequence.

Submitted by:	jbh@ (suggested by)
Sponsored by:	Yahoo! Inc.
MFC'ing to 9.2.