USB: EHCI: remove CNS3xxx EHCI platform driver

The users have been converted to use the ehci platform driver instead, thus
making the ehci-cns3xxx driver obsolete, so remove it.

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>