sata_rcar: Document deprecated "renesas,rcar-sata"

Commit e67adb4e ("sata_rcar: Add R-Car Gen2 SATA PHY support")
deprecated "renesas,rcar-sata" in favor of "renesas,sata-r8a7779", but
the deprecated value was never documented in the binding documentation,
while it is still in active use.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NSimon Horman <horms+renesas@verge.net.au>
Signed-off-by: NTejun Heo <tj@kernel.org>

Documentation/devicetree/bindings/ata/sata_rcar.txt

@@ -3,6 +3,7 @@
 Required properties:
 - compatible		: should contain one of the following:
 			  - "renesas,sata-r8a7779" for R-Car H1
+			    ("renesas,rcar-sata" is deprecated)
 			  - "renesas,sata-r8a7790-es1" for R-Car H2 ES1
 			  - "renesas,sata-r8a7790" for R-Car H2 other than ES1
 			  - "renesas,sata-r8a7791" for R-Car M2-W