doc: Bring in the FIT examples

Convert these to rST format and add them to the index.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/usage/fit/kernel.rst b/doc/usage/fit/kernel.rst
new file mode 100644
index 0000000..012a81e
--- /dev/null
+++ b/doc/usage/fit/kernel.rst
@@ -0,0 +1,93 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Single kernel
+=============
+
+::
+
+    /dts-v1/;
+
+    / {
+        description = "Simple image with single Linux kernel";
+        #address-cells = <1>;
+
+        images {
+            kernel {
+                description = "Vanilla Linux kernel";
+                data = /incbin/("./vmlinux.bin.gz");
+                type = "kernel";
+                arch = "ppc";
+                os = "linux";
+                compression = "gzip";
+                load = <00000000>;
+                entry = <00000000>;
+                hash-1 {
+                    algo = "crc32";
+                };
+                hash-2 {
+                    algo = "sha1";
+                };
+            };
+        };
+
+        configurations {
+            default = "config-1";
+            config-1 {
+                description = "Boot Linux kernel";
+                kernel = "kernel";
+            };
+        };
+    };
+
+
+For x86 a setup node is also required: see x86-fit-boot::
+
+    /dts-v1/;
+
+    / {
+        description = "Simple image with single Linux kernel on x86";
+        #address-cells = <1>;
+
+        images {
+            kernel {
+                description = "Vanilla Linux kernel";
+                data = /incbin/("./image.bin.lzo");
+                type = "kernel";
+                arch = "x86";
+                os = "linux";
+                compression = "lzo";
+                load = <0x01000000>;
+                entry = <0x00000000>;
+                hash-2 {
+                    algo = "sha1";
+                };
+            };
+
+            setup {
+                description = "Linux setup.bin";
+                data = /incbin/("./setup.bin");
+                type = "x86_setup";
+                arch = "x86";
+                os = "linux";
+                compression = "none";
+                load = <0x00090000>;
+                entry = <0x00090000>;
+                hash-2 {
+                    algo = "sha1";
+                };
+            };
+        };
+
+        configurations {
+            default = "config-1";
+            config-1 {
+                description = "Boot Linux kernel";
+                kernel = "kernel";
+                setup = "setup";
+            };
+        };
+    };
+
+Note: the above assumes a 32-bit kernel. To directly boot a 64-bit kernel,
+change both arch values to "x86_64". U-Boot will then change to 64-bit mode
+before booting the kernel (see boot_linux_kernel()).