libata: add R-Car SATA driver

Add Renesas R-Car on-chip 3Gbps SATA controller driver.

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
[Sergei: few bugs fixed, significant cleanup]
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>