cmd: provide command to display SMBIOS information

U-Boot can either generated an SMBIOS table or copy it from a prior boot
stage, e.g. QEMU.

Provide a command to display the SMBIOS information.

Currently only type 1 and 2 are translated to human readable text.
Other types may be added later. Currently only a hexdump and the list of
strings is provided for these.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>