ahci: make ahci_transmit_led_message into a function pointer

Create a new ata_port_operations function pointer called
transmit_led_message and give it the default value of
ahci_transmit_led_message. This allows AHCI controllers with
non-standard LED interfaces to use the existing em_ interface.

Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/libata.h

@@ -910,6 +910,9 @@ struct ata_port_operations {
 	ssize_t (*sw_activity_show)(struct ata_device *dev, char *buf);
 	ssize_t (*sw_activity_store)(struct ata_device *dev,
 				     enum sw_activity val);
+	ssize_t (*transmit_led_message)(struct ata_port *ap, u32 state,
+					ssize_t size);
+
 	/*
 	 * Obsolete
 	 */