staging: dgap: Only read config file dgap.conf once

The config file is currently read for each board found.
It only needs to be read one time. The buffer it is read
into can now be freed immediately after it is parsed
instead of at driver unload time.

Signed-off-by: Mark Hounschell <markh@compro.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>