git: kernel - Add workaround for errata #721 on AMD cpus (found by Matt Dillon)

[Thomas Nikolajsen]

>commit afea4d5a3cf396976e5b778f8477d972e8c29735
>Author: Matthew Dillon <dillon at apollo.backplane.com>
>Date:   Fri Mar 23 15:49:54 2012 -0700
>
>    kernel - Add workaround for errata #721 on AMD cpus (found by Matt Dillon)
..
>+                               kprintf("Errata 721 workaround installed\n");

Could we put message under bootverbose?

Also message seems to be missing one instance in log:
it only shows for APs:
log buffer isn't set up yet when code is executed for BSP.
Guess fewer users will be confused if we don't show message by default.

 -thomas