usb: chipidea: add identification registers access APIs

Using hw_write_id_reg and hw_read_id_reg to write and read identification
registers contents, they can be used to get controller information, change
some system configurations, and so on.

Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>