net: phy: dp83867: Add device tree bindings and documentation

Add the device tree bindings and the accompanying documentation
for the TI DP83867 Giga bit ethernet phy driver.

The original document was from:
    [commit 2a10154abcb75ad0d7b6bfea6210ac743ec60897 from the Linux kernel]

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Tested-by: Mugunthan V N <mugunthanvnm@ti.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

doc/device-tree-bindings/net/ti,dp83867.txt

+* Texas Instruments - dp83867 Giga bit ethernet phy
+
+Required properties:
+	- reg - The ID number for the phy, usually a small integer
+	- ti,rx-internal-delay - RGMII Recieve Clock Delay - see dt-bindings/net/ti-dp83867.h
+		for applicable values
+	- ti,tx-internal-delay - RGMII Transmit Clock Delay - see dt-bindings/net/ti-dp83867.h
+		for applicable values
+	- ti,fifo-depth - Transmitt FIFO depth- see dt-bindings/net/ti-dp83867.h
+		for applicable values
+
+Default child nodes are standard Ethernet PHY device
+nodes as described in doc/devicetree/bindings/net/ethernet.txt
+
+Example:
+
+	ethernet-phy@0 {
+		reg = <0>;
+		ti,rx-internal-delay = <DP83867_RGMIIDCTL_2_25_NS>;
+		ti,tx-internal-delay = <DP83867_RGMIIDCTL_2_75_NS>;
+		ti,fifo-depth = <DP83867_PHYCR_FIFO_DEPTH_4_B_NIB>;
+	};
+
+Datasheet can be found:
+http://www.ti.com/product/DP83867IR/datasheet

include/dt-bindings/net/ti-dp83867.h

+/*
+ * TI DP83867 PHY drivers
+ *
+ * SPDX-License-Identifier:	GPL-2.0
+ *
+ */
+
+#ifndef _DT_BINDINGS_TI_DP83867_H
+#define _DT_BINDINGS_TI_DP83867_H
+
+/* PHY CTRL bits */
+#define DP83867_PHYCR_FIFO_DEPTH_3_B_NIB	0x00
+#define DP83867_PHYCR_FIFO_DEPTH_4_B_NIB	0x01
+#define DP83867_PHYCR_FIFO_DEPTH_6_B_NIB	0x02
+#define DP83867_PHYCR_FIFO_DEPTH_8_B_NIB	0x03
+
+/* RGMIIDCTL internal delay for rx and tx */
+#define DP83867_RGMIIDCTL_250_PS	0x0
+#define DP83867_RGMIIDCTL_500_PS	0x1
+#define DP83867_RGMIIDCTL_750_PS	0x2
+#define DP83867_RGMIIDCTL_1_NS		0x3
+#define DP83867_RGMIIDCTL_1_25_NS	0x4
+#define DP83867_RGMIIDCTL_1_50_NS	0x5
+#define DP83867_RGMIIDCTL_1_75_NS	0x6
+#define DP83867_RGMIIDCTL_2_00_NS	0x7
+#define DP83867_RGMIIDCTL_2_25_NS	0x8
+#define DP83867_RGMIIDCTL_2_50_NS	0x9
+#define DP83867_RGMIIDCTL_2_75_NS	0xa
+#define DP83867_RGMIIDCTL_3_00_NS	0xb
+#define DP83867_RGMIIDCTL_3_25_NS	0xc
+#define DP83867_RGMIIDCTL_3_50_NS	0xd
+#define DP83867_RGMIIDCTL_3_75_NS	0xe
+#define DP83867_RGMIIDCTL_4_00_NS	0xf
+
+#endif