system: return legacy board name

system: return legacy board name

The system board call returns the verbose model string instead of the
board name. Unfortunately we have not yet estabkushed clear convention
regarding device-tree 'compatible' or 'model' property and sysupgrade
image name (same accounts for scraping /proc/cpuinfo on legacy
targets). This is odd as the idea was to return information needed to
identify the right sysupgrade image. On most targets we got a large
shell-script which translates either /proc/cpuinfo or the 'model'
property back into the board name used here. Hence
/tmp/sysinfo/board_name should be returned instead of
/tmp/sysinfo/model for the board ubus call as well.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>