drivers/usb : Define usb control register mask for w1c bits

Define and use CONTROL_REGISTER_W1C_MASK to make sure that
w1c bits of usb control register do not get reset while
writing any other bit

Signed-off-by: Nikhil Badola <nikhil.badola@freescale.com>
Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>