Some changes around hot-plug and interface power-management:

• use ATA_SE_EXCHANGED (SError.DIAG.X) bit to detect hot-plug events when

power-management enabled and ATA_SE_PHY_CHANGED (SError.DIAG.N) can't be
trusted;

• on controllers supporting staggered spin-up (SS) put unused channels

into Listen state instead of Off. It should still save some power, but
allow plug-in events to be detected;

• on controllers supporting cold presence detection (CPD), when power

management enabled, use CPD events to detect hot-plug in addition to PHY
events.