libata: separate out ata_wait_ready() and implement ata_wait_after_reset()

Factor out waiting logic (which is common to all ATA controllers) from
ata_sff_wait_ready() into ata_wait_ready().  ata_wait_ready() takes
@check_ready function pointer and uses it to poll for readiness.  This
allows non-SFF controllers to use ata_wait_ready() to wait for link
readiness.

This patch also implements ata_wait_after_reset() - generic version of
ata_sff_wait_after_reset() - using ata_wait_ready().

ata_sff_wait_ready() is reimplemented using ata_wait_ready() and
ata_sff_check_ready().  Functionality remains the same.

Signed-off-by: Tejun Heo <htejun@gmail.com>
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 11b5f67..08af43e 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -81,6 +81,8 @@
 				     int dma_dir, struct scatterlist *sg,
 				     unsigned int n_elem, unsigned long timeout);
 extern unsigned int ata_do_simple_cmd(struct ata_device *dev, u8 cmd);
+extern int ata_wait_ready(struct ata_link *link, unsigned long deadline,
+			  int (*check_ready)(struct ata_link *link));
 extern int ata_dev_read_id(struct ata_device *dev, unsigned int *p_class,
 			   unsigned int flags, u16 *id);
 extern int ata_dev_reread_id(struct ata_device *dev, unsigned int readid_flags);