ar71xx, ramips: reduce CPU load and flickering on devices using rsslieds

Polling every 40ms causes more than 10% CPU load on weak devices. An
interval of 200ms is much more reasonable.

Signed-off-by: Martin Weinelt <martin@darmstadt.freifunk.net>
[Matthias Schiffer: adapt OpenWrt patch; add ramips; extend commit message]
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>