sysinfo: Provide a default driver to set SMBIOS values

Some boards want to specify the manufacturer or product name but do not
need to have their own sysinfo driver.

Add a default driver which provides a way to specify this SMBIOS
information in the devicetree, without needing any board-specific
functionality.

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