MFC r224270:

MFC r224270:
 - Use mutex to serialize index/data register pair usage, when
accessing SATA registers. Unserialized access under heavy load caused
wrong speed reporting and potentially could cause device loss.
 - To free memory and other resources (including above), allocated
during chipinit() method call on attach, add new chipdeinit() method,
called during driver detach.

git-svn-id: svn://svn.freebsd.org/base/stable/8@224490 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f