MIPS: BCM47XX: Add support for Linksys E2500 V3

It's a BCM5358 based home WiFi router. 16 MiB flash, 64 MiB RAM, BCM5325
switch, on-SoC 802.11n radio.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>