smbios: Add documentation and devicetree binding

Add information about how to set SMBIOS properties using the devicetree.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/doc/arch/x86.rst b/doc/arch/x86.rst
index c6b70ce..cc307aa 100644
--- a/doc/arch/x86.rst
+++ b/doc/arch/x86.rst
@@ -740,6 +740,14 @@
 production environments. Also it is not currently part of the automated tests
 so may break in the future.
 
+SMBIOS tables
+-------------
+
+To generate SMBIOS tables in U-Boot, for use by the OS, enable the
+CONFIG_GENERATE_SMBIOS_TABLE option. The easiest way to provide the values to
+use is via the device tree. For details see
+device-tree-bindings/sysinfo/smbios.txt
+
 TODO List
 ---------
 - Audio