dt-bindings: ata: drop unused Exynos SATA bindings

The Samsung Exynos SoC SATA bindings are not implemented in the kernel,
not used and superseded by generic
Documentation/devicetree/bindings/ata/ahci-platform.txt bindings.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210811083859.28234-1-krzysztof.kozlowski@canonical.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/ata/exynos-sata.txt

-* Samsung AHCI SATA Controller
-
-SATA nodes are defined to describe on-chip Serial ATA controllers.
-Each SATA controller should have its own node.
-
-Required properties:
-- compatible		: compatible list, contains "samsung,exynos5-sata"
-- interrupts		: <interrupt mapping for SATA IRQ>
-- reg			: <registers mapping>
-- samsung,sata-freq	: <frequency in MHz>
-- phys			: Must contain exactly one entry as specified
-			  in phy-bindings.txt
-- phy-names		: Must be "sata-phy"
-
-Optional properties:
-- clocks		: Must contain an entry for each entry in clock-names.
-- clock-names		: Shall be "sata" for the external SATA bus clock,
-			  and "sclk_sata" for the internal controller clock.
-
-Example:
-	sata@122f0000 {
-		compatible = "snps,dwc-ahci";
-		samsung,sata-freq = <66>;
-		reg = <0x122f0000 0x1ff>;
-		interrupts = <0 115 0>;
-		clocks = <&clock 277>, <&clock 143>;
-		clock-names = "sata", "sclk_sata";
-		phys = <&sata_phy>;
-		phy-names = "sata-phy";
-	};