libata: cleanup device sleep capability detection

Move the code to retrieve the device sleep capability and timings out of
ata_dev_configure() into the helper function ata_dev_config_devslp().
While at it, mark the device as supporting the device sleep capability
only if the sata settings page was retrieved successfully to ensure that
the timing information is correctly initialized.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210816014456.2191776-5-damien.lemoal@wdc.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>