ar71xx: deactivate some boards with too small kernel partitions

ar71xx: deactivate some boards with too small kernel partitions

This affects the following boards:
 * dr344
 * archer-c58-v1
 * archer-c60-v1
 * tl-wr902ac-v1
 * tl-wr942n-v1
 * ubnt-uap-pro
 * ubnt-unifi-outdoor-plus

The build fails for any of these boards because the resulting kernel
image will not fit into the kernel partition.

When CONFIG_KERNEL_KALLSYMS  is not set it could be that the kernel will
fit onto the board again, this is the case for release images.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>