Reimplement controller-wide PM.  ata_host_set_suspend/resume() are
defined to suspend and resume a host_set.  While suspended, EHs for
all ports in the host_set are pegged using ATA_FLAG_SUSPENDED and
frozen.

Because SCSI device hotplug is done asynchronously against the rest of
libata EH and the same mutex is used when adding new device, suspend
cannot wait for hotplug to complete.  So, if SCSI device hotplug is in
progress, suspend fails with -EBUSY.

In most cases, host_set resume is followed by device resume.  As each
resume operation requires a reset, a single host_set-wide resume
operation may result in multiple resets.  To avoid this, resume waits
upto 1 second giving PM to request resume for devices.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>