libata: implement sata_link_scr_lpm() and make ata_dev_set_feature() global

Link power management is about to be reimplemented.  Prepare for it.

* Implement sata_link_scr_lpm().

* Drop static from ata_dev_set_feature() and make it available to
  other libata files.

* Trivial whitespace adjustments.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/include/linux/libata.h b/include/linux/libata.h
index c5bdc90..7770eeb 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -952,6 +952,8 @@
 			const unsigned long *params, unsigned long deadline);
 extern int sata_link_resume(struct ata_link *link, const unsigned long *params,
 			    unsigned long deadline);
+extern int sata_link_scr_lpm(struct ata_link *link, enum ata_lpm_policy policy,
+			     bool spm_wakeup);
 extern int sata_link_hardreset(struct ata_link *link,
 			const unsigned long *timing, unsigned long deadline,
 			bool *online, int (*check_ready)(struct ata_link *));