10773 sata: NULL pointer errors
Reviewed by: Andy Stormont <astormont@racktopsystems.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Dan McDonald <danmcd@joyent.com>

PSARC/2009/394 SATA Framework Port Multiplier Support
6422924 sata framework has to support port multipliers
6691950 ahci driver needs to support SIL3726/4726 SATA port multiplier