dt-bindings: power: Add ZynqMP power domain bindings

Add documentation to describe ZynqMP power domain bindings.
Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>
Signed-off-by: Jolly Shah <jolly.shah@xilinx.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

Documentation/devicetree/bindings/power/xlnx,zynqmp-genpd.txt

+-----------------------------------------------------------
+Device Tree Bindings for the Xilinx Zynq MPSoC PM domains
+-----------------------------------------------------------
+The binding for zynqmp-power-controller follow the common
+generic PM domain binding[1].
+
+[1] Documentation/devicetree/bindings/power/power_domain.txt
+
+== Zynq MPSoC Generic PM Domain Node ==
+
+Required property:
+ - Below property should be in zynqmp-firmware node.
+ - #power-domain-cells:	Number of cells in a PM domain specifier. Must be 1.
+
+Power domain ID indexes are mentioned in
+include/dt-bindings/power/xlnx-zynqmp-power.h.
+
+-------
+Example
+-------
+
+firmware {
+	zynqmp_firmware: zynqmp-firmware {
+		...
+		#power-domain-cells = <1>;
+		...
+	};
+};
+
+sata {
+	...
+	power-domains = <&zynqmp_firmware 28>;
+	...
+};

include/dt-bindings/power/xlnx-zynqmp-power.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  Copyright (C) 2018 Xilinx, Inc.
+ */
+
+#ifndef _DT_BINDINGS_ZYNQMP_POWER_H
+#define _DT_BINDINGS_ZYNQMP_POWER_H
+
+#define		PD_USB_0	22
+#define		PD_USB_1	23
+#define		PD_TTC_0	24
+#define		PD_TTC_1	25
+#define		PD_TTC_2	26
+#define		PD_TTC_3	27
+#define		PD_SATA		28
+#define		PD_ETH_0	29
+#define		PD_ETH_1	30
+#define		PD_ETH_2	31
+#define		PD_ETH_3	32
+#define		PD_UART_0	33
+#define		PD_UART_1	34
+#define		PD_SPI_0	35
+#define		PD_SPI_1	36
+#define		PD_I2C_0	37
+#define		PD_I2C_1	38
+#define		PD_SD_0		39
+#define		PD_SD_1		40
+#define		PD_DP		41
+#define		PD_GDMA		42
+#define		PD_ADMA		43
+#define		PD_NAND		44
+#define		PD_QSPI		45
+#define		PD_GPIO		46
+#define		PD_CAN_0	47
+#define		PD_CAN_1	48
+#define		PD_GPU		58
+#define		PD_PCIE		59
+
+#endif