block: implement runtime pm strategy

When a request is added:
    If device is suspended or is suspending and the request is not a
    PM request, resume the device.

When the last request finishes:
    Call pm_runtime_mark_last_busy().

When pick a request:
    If device is resuming/suspending, then only PM request is allowed
    to go.

Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
sd: change to auto suspend mode

Uses block layer runtime pm helper functions in
scsi_runtime_suspend/resume.
Remove scsi_autopm_* from sd open/release path and check_events path.
And remove the quiesce call in runtime suspend path, as we know there is
no request to quiesce for the device.

Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>