usb: renesas_usbhs: add support for CNEN bit

For some SoC, CNEN must be set for USB Device mode operation.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>