usb: dwc2: Add functions to set and clear force mode

Added functions to set force mode for host and device. These functions
will check the current mode and only force if needed thus avoiding
unnecessary force mode delays. However clearing the mode is currently
done unconditionally and with the delay in place. This is needed during
the connector ID status change interrupt in order to ensure that the
mode has changed properly. This preserves the old behavior only for this
case. The warning comment about this is moved into the clear mode
condition.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>