ARM: cns3xxx: use ehci platform driver

This patch converts the cns3xxx platform to use the ehci-platform driver
instead of the ehci-cns3xxx platform driver.

The ehci-platform driver is provided with power_{on,off} callbacks to ensure
proper block gating and USB configuration of the EHCI controller.

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>