of: Add NVIDIA Tegra SATA controller binding

This patch adds device tree binding documentation for the SATA
controller found on NVIDIA Tegra SoCs.
Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

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

+Tegra124 SoC SATA AHCI controller
+
+Required properties :
+- compatible : "nvidia,tegra124-ahci".
+- reg : Should contain 2 entries:
+  - AHCI register set (SATA BAR5)
+  - SATA register set
+- interrupts : Defines the interrupt used by SATA
+- clocks : Must contain an entry for each entry in clock-names.
+  See ../clocks/clock-bindings.txt for details.
+- clock-names : Must include the following entries:
+  - sata
+  - sata-oob
+  - cml1
+  - pll_e
+- resets : Must contain an entry for each entry in reset-names.
+  See ../reset/reset.txt for details.
+- reset-names : Must include the following entries:
+  - sata
+  - sata-oob
+  - sata-cold
+- phys : Must contain an entry for each entry in phy-names.
+  See ../phy/phy-bindings.txt for details.
+- phy-names : Must include the following entries:
+  - sata-phy : XUSB PADCTL SATA PHY
+- hvdd-supply : Defines the SATA HVDD regulator
+- vddio-supply : Defines the SATA VDDIO regulator
+- avdd-supply : Defines the SATA AVDD regulator
+- target-5v-supply : Defines the SATA 5V power regulator
+- target-12v-supply : Defines the SATA 12V power regulator