It is useful to be able to see the MTRR setup in U-Boot. Add a command
to list the state of the variable MTRR registers and allow them to be
changed.
Update the documentation to list some of the available commands.
This does not support fixed MTRRs as yet.
Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
