scsi: sd: add runtime pm to open / release

This add a very conservative implementation of runtime PM to the sd scsi
driver: Resume when opened (mounted) and suspend when released (unmounted).

often event polling for block devicesneeds to be disabled in order to
be able to suspend:
echo 0 > /sys/module/block/parameters/events_dfl_poll_msecs

This still doesn't enable runtime PM by default. It can be enabled
via the standard Linux power user interface, like:
echo 1000 > /sys/bus/scsi/devices/0:0:0:0/power/autosuspend_delay_ms
echo auto > /sys/bus/scsi/devices/0:0:0:0/power/control

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
2 jobs for sd_pm_1 in 70 minutes and 9 seconds (queued for 1 second)