AHCI driver port update - working with hot-plug

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

    The AHCI driver is now working for DISK and ATAPI attachments, and
    hot-plug also now works.

    All major features except port multiplier support are now operational.

    The hot-plug support is very recent and probably needs some tweaking,
    but it works with my basic tests.

    Port multiplier support is upcoming, I expect to get it written fairly
    quickly once I get the PM hardware I've ordered.


    		TESTING (not for the light hearted)


    Both the AHCI and the NATA devices may be specified in kernel builds,
    and AHCI can be loaded as a module too which is how I would suggest
    people use it for the moment.  That is, you can leave NATA in your
    kernel build and load AHCI as a module in /boot/loader.conf:

	ahci_load="YES"

    Note that you must do a full kernel build and install to make sure
    everything is in sync.

    Your ATA disk devices, for example, 'ad4', will become SCSI disk devices,
    for example 'da0'.  You thus need to modify your /etc/fstab and if you
    are using a boot + root HAMMER configuration you also need to adjust
    the root filesystem mount line in your /boot/loader.conf.

    It's fairly easy to get it wrong and for the system to not be able to
    find the root mount, in which case carefully specifying it on the
    kernel's mountroot> line should get you into single-user.

    I am particularly interested in systems which have a separate,
    traditional non-AHCI ATA device as well as one or more AHCI devices,
    I'd like to know that AHCI picks up the AHCI devices and NATA picks
    up the non-AHCI devices properly.

						-Matt