USB: PLAT_ORION fulfils USB_ARCH_HAS_EHCI

The various Orion SoCs, i.e. orion5x, kirkwood, dove, mv78xx0
and 370/XP have EHCI. Make sure USB_ARCH_HAS_EHCI reflects this.

Reported-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>