doc: uefi: add HTTP Boot support

This adds the description about HTTP Boot.

[Ilias add the new EFI_HTTP_BOOT option in docs]
Lore: https://lore.kernel.org/u-boot/20231110042542.3797301-1-masahisa.kojima@linaro.org/T/#m36acf922a888cc14f74e823ec57bacd9f977194e
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

doc/develop/uefi/uefi.rst

@@ -642,6 +642,40 @@ UEFI variables. Booting according to these variables is possible via::
 As of U-Boot v2020.10 UEFI variables cannot be set at runtime. The U-Boot
 command 'efidebug' can be used to set the variables.
 
+UEFI HTTP Boot
+~~~~~~~~~~~~~~
+
+HTTP Boot provides the capability for system deployment and configuration
+over the network. HTTP Boot can be activated by specifying::
+
+    CONFIG_EFI_HTTP_BOOT
+
+Enabling that will automatically select::
+
+    CONFIG_CMD_DNS
+    CONFIG_CMD_WGET
+    CONFIG_BLKMAP
+
+Set up the load option specifying the target URI::
+
+    efidebug boot add -u 1 netinst http://foo/bar
+
+When this load option is selected as boot selection, resolve the
+host ip address by dns, then download the file with wget.
+If the downloaded file extension is .iso or .img file, efibootmgr tries to
+mount the image and boot with the default file(e.g. EFI/BOOT/BOOTAA64.EFI).
+If the downloaded file is PE-COFF image, load the downloaded file and
+start it.
+
+The current implementation tries to resolve the IP address as a host name.
+If the uri is like "http://192.168.1.1/foobar",
+the dns process tries to resolve the host "192.168.1.1" and it will
+end up with "host not found".
+
+We need to preset the "httpserverip" environment variable to proceed the wget::
+
+    setenv httpserverip 192.168.1.1
+
 Executing the built in hello world application
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~