doc: add bind/unbind command documentation

Add documentation in doc/drivel-model for the bind/unbind command.
Part of this documentation is extracted from original patch commit
message:
commit 49c752c93a ("cmd: Add bind/unbind commands to bind a device to a driver from the command line")

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

doc/driver-model/bind.rst

@@ -0,0 +1,49 @@
+.. SPDX-License-Identifier: GPL-2.0+
+.. sectionauthor:: Patrice Chotard <patrice.chotard@st.com>
+
+Binding/unbinding a driver
+==========================
+
+This document aims to describe the bind and unbind commands.
+
+For debugging purpose, it should be useful to bind or unbind a driver from
+the U-boot command line.
+
+The unbind command calls the remove device driver callback and unbind the
+device from its driver.
+
+The bind command binds a device to its driver.
+
+In some cases it can be useful to be able to bind a device to a driver from
+the command line.
+The obvious example is for versatile devices such as USB gadget.
+Another use case is when the devices are not yet ready at startup and
+require some setup before the drivers are bound (ex: FPGA which bitsream is
+fetched from a mass storage or ethernet)
+
+usage:
+
+bind <node path> <driver>
+bind <class> <index> <driver>
+
+unbind <node path>
+unbind <class> <index>
+unbind <class> <index> <driver>
+
+Where:
+ - <node path> is the node's device tree path
+ - <class> is one of the class available in the list given by the "dm uclass"
+   command or first column of "dm tree" command.
+ - <index> is the index of the parent's node (second column of "dm tree" output).
+ - <driver> is the driver name to bind given by the "dm drivers" command or the by
+   the fourth column of "dm tree" output.
+
+example:
+
+bind usb_dev_generic 0 usb_ether
+unbind usb_dev_generic 0 usb_ether
+or
+unbind eth 1
+
+bind /ocp/omap_dwc3@48380000/usb@48390000 usb_ether
+unbind /ocp/omap_dwc3@48380000/usb@48390000

doc/driver-model/index.rst

@@ -6,6 +6,7 @@ Driver Model
 .. toctree::
    :maxdepth: 2
 
+   bind
    debugging
    design
    ethernet