ipmi ipmb support

From: Yuri <yuri_at_aetern.org>
Date: Sun, 26 Jun 2022 19:00:54 UTC
Hi,

I have put an initial attempt at implementing the IPMB support in ipmi
driver:

https://reviews.freebsd.org/D35605

It is pretty naive in that it does NOT wait for SMS_ATTN from BMC, nor
does it any checks that data returned by GET_MSG from satellite
controller corresponds to SEND_MSG we sent.  Good news is that it works
flawlessly for me on some system that I have tested, primarily HPE
ProLiant DL380 Gen10.

If anyone is interested, please review/test/possibly integrate with a
TODO for making it more robust.