libata: implement PMP helpers

Implement helpers to test whether PMP is supported, attached and
determine pmp number to use when issuing SRST to a link.  While at it,
move ata_is_host_link() so that it's together with the two new PMP
helpers.

This change simplifies LLDs and helps making PMP support optional.

Signed-off-by: Tejun Heo <htejun@gmail.com>

drivers/ata/libata-pmp.c

@@ -411,7 +411,7 @@ int sata_pmp_attach(struct ata_device *dev)
 	int rc;
 
 	/* is it hanging off the right place? */
-	if (!(ap->flags & ATA_FLAG_PMP)) {
+	if (!sata_pmp_supported(ap)) {
 		ata_dev_printk(dev, KERN_ERR,
 			       "host does not support Port Multiplier\n");
 		return -EINVAL;
@@ -876,7 +876,7 @@ static int sata_pmp_eh_recover(struct ata_port *ap)
 
  retry:
 	/* PMP attached? */
-	if (!ap->nr_pmp_links) {
+	if (!sata_pmp_attached(ap)) {
 		rc = ata_eh_recover(ap, ops->prereset, ops->softreset,
 				    ops->hardreset, ops->postreset, NULL);
 		if (rc) {
@@ -983,7 +983,7 @@ static int sata_pmp_eh_recover(struct ata_port *ap)
 	if (ap->pflags & ATA_PFLAG_UNLOADING)
 		return rc;
 
-	if (!ap->nr_pmp_links)
+	if (!sata_pmp_attached(ap))
 		goto retry;
 
 	if (--pmp_tries) {