usb: chipidea: export interrupt enable and status register read functions

This patch moves usb interrupt enable and status register read functions
from udc driver to core driver to use them in all ci drivers.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Li Jun <b47624@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>