ATA: sata_mv: Add device tree support

Add support for instantiating this driver from device tree, and add
the necassary DT information to the kirkwood.dtsi file.

This is based on previous work by Michael Walle and Jason Cooper.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Josh Coombs <josh.coombs@gmail.com>