MIPS: Loongson 1B: use ehci-platform instead of ehci-ls1x.

The Loongson 1B EHCI driver does nothing more than what the EHCI platform
driver already does, so use the generic implementation.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>