MIPS: BCM63xx: enable EHCI for DWV-S0 board

BCM6358 SoCs have OHCI and EHCI controllers that share the same USB ports.
Therefore, the board should also have EHCI enabled.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>