sata_rcar: Add R-Car Gen2 SATA PHY support

R-Car Gen2 SoCs have a different PHY which is not compatible
with the older R-Car H1 (R8A7779) version.
This adds OF/platform device id tables and PHY initialization
callbacks for the following Gen2 SoCs:
  * R-Car H2: R8A7790;
  * R-Car M2: R8A7791.

PHY initialization method is chosen based on the device id.
Default PHY settings are applied for Gen2 SoCs, which should
suit the Gen2 boards available.

While at it, this also adds "sata-r8a7779" compatibility string
for R8A7779 SATA, while keeping the old one for compatibility.

Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
Signed-off-by: Tejun Heo <tj@kernel.org>