Use the DMI data available in sysfs to extract manufacturer and model info
and write it to /tmp/sysinfo/.
The data will be picked up by board_detect and can be used by e.g. LuCI to
display a more appropriate model description.
On an APU board the files will contain the following values:
# cat /tmp/sysinfo/model
PC Engines APU
# cat /tmp/sysinfo/board_name
pc-engines-apu
Signed-off-by: Jo-Philipp Wich <jo@mein.io>