The EFI memory map is passed from the stub to U-Boot in a table. Add a
command to display it in a vaguely readable fashion.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested on QEMU
Tested-by: Bin Meng <bmeng.cn@gmail.com>