Kernel partition increase to 4 MiBs for Netgear WNDR3700v4 and WNDR4300
routers breaks sysupgrade image compatibility with ar71xx builds.
Therefore, SUPPORTED_DEVICES variable has to be removed for both devices
from target makefile.
Reported-by: DENG Qingfang <dengqf6@mail2.sysu.edu.cn>
Signed-off-by: Michal Cieslakiewicz <michal.cieslakiewicz@wp.pl>