sata_inic162x: add / update constants

* add a bunch of constants, most are from the datasheet, a few
  undocumented ones are from initio's modified driver

* HCTL_PWRDWN is bit 12 not 13

This is in preparation of further inic162x updates.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>