dfu: tftp: Kconfig: Add Kconfig entry for dfu tftp feature

The dfu tftp feature can be now enabled via Kconfig. This
commit provides necessary code for it.

Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
1 file changed