doc: boards: x86: Add generic net_boot.rst

Add generic documentation for the Network Boot over PXE.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>

boards/x86/common/net_boot.rst

@@ -0,0 +1,88 @@
+Prepare Linux host
+------------------
+
+#. Install DHCP, TFTP servers. For example ``dnsmasq``
+
+   .. code-block:: console
+
+      $ sudo apt-get install dnsmasq
+
+#. Configure DHCP server. Configuration for ``dnsmasq`` is below:
+
+   .. code-block:: console
+
+      # Only listen to this interface
+      interface=eno2
+      dhcp-range=10.1.1.20,10.1.1.30,12h
+
+#. Configure TFTP server.
+
+   .. code-block:: console
+
+      # tftp
+      enable-tftp
+      tftp-root=/srv/tftp
+      dhcp-boot=zephyr.efi
+
+   ``zephyr.efi`` is a Zephyr EFI binary created above.
+
+#. Copy the Zephyr EFI image :file:`zephyr/zephyr.efi` to the
+   :file:`/srv/tftp` folder.
+
+    .. code-block:: console
+
+       $ cp zephyr/zephyr.efi /srv/tftp
+
+
+#. TFTP root should be looking like:
+
+   .. code-block:: console
+
+      $ tree /srv/tftp
+      /srv/tftp
+      └── zephyr.efi
+
+#. Restart ``dnsmasq`` service:
+
+   .. code-block:: console
+
+      $ sudo systemctl restart dnsmasq.service
+
+Prepare the board for network boot
+----------------------------------
+
+#. Enable PXE network from BIOS settings.
+
+#. Make network boot as the first boot option.
+
+Booting the board
+-----------------
+
+#. Connect the board to the host system using the serial cable and
+   configure your host system to watch for serial data. See board's
+   website for more information.
+
+   .. note::
+      Use a baud rate of 115200.
+
+#. Power on the the board.
+
+#. Verify that the board got an IP address. Run from the Linux host:
+
+   .. code-block:: console
+
+      $ journalctl -f -u dnsmasq
+      dnsmasq-dhcp[5386]: DHCPDISCOVER(eno2) 00:07:32:52:25:88
+      dnsmasq-dhcp[5386]: DHCPOFFER(eno2) 10.1.1.28 00:07:32:52:25:88
+      dnsmasq-dhcp[5386]: DHCPREQUEST(eno2) 10.1.1.28 00:07:32:52:25:88
+      dnsmasq-dhcp[5386]: DHCPACK(eno2) 10.1.1.28 00:07:32:52:25:88
+
+#. Verify that network booting is started:
+
+   .. code-block:: console
+
+      $ journalctl -f -u dnsmasq
+      dnsmasq-tftp[5386]: sent /srv/tftp/zephyr.efi to 10.1.1.28
+
+#. When the boot process completes, you have finished booting the
+   Zephyr application image.