usb: mtu3: use FORCE/RG_IDDIG to implement manual DRD switch

In order to keep manual DRD switch independent on IDDIG interrupt,
make use of FORCE/RG_IDDIG instead of IDDIG EINT interrupt to
implement manual DRD switch function.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>