libata project: START STOP UNIT translation

If anybody is looking for SATA kernel hacking project, here's a small and self-contained one:

Implement the translation of SCSI command START STOP UNIT in drivers/scsi/libata-scsi.c.

Among other things, this will give people with SATA power management capabilities.

START STOP UNIT is described at

	http://www.t10.org/ftp/t10/drafts/sbc2/sbc2r16.pdf

The translation of START STOP UNIT from SCSI to ATA is described at

	http://www.t10.org/ftp/t10/drafts/sat/sat-r04.pdf

The relevant ATA commands you will be using are documented at

	http://www.t13.org/docs2004/d1532v1r4b-ATA-ATAPI-7.pdf

More info on SATA hacking can be had by reading
http://linux.yyz.us/sata/devel.html

or by reading drivers/scsi/libata*.[ch], include/linux/libata.h, include/linux/ata.h, and drivers/scsi/sata_*.c.