x86: coreboot: Add a command to check and update CMOS RAM

Coreboot tables provide information about the CMOS-RAM checksum. Add a
command which can check and update this.

With this it is possible to adjust CMOS-RAM settings and tidy up the
checksum afterwards.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index db71711..b7c80ef 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -43,6 +43,7 @@
    cmd/bootz
    cmd/button
    cmd/cat
+   cmd/cbcmos
    cmd/cbsysinfo
    cmd/cedit
    cmd/cli