usb: mtu3: fix the issue about SetFeature(U1/U2_Enable)

Fix the issue: device doesn't accept LGO_U1/U2:
1. set SW_U1/U2_ACCEPT_ENABLE to eanble controller to accept LGO_U1/U2
    by default;
2. enable/disable controller to initiate requests for transition into
    U1/U2 by SW_U1/U2_REQUEST_ENABLE instead of SW_U1/U2_ACCEPT_ENABLE;

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