usb: dwc3: Set GUSB3PIPECTL_SUSPHY only after connection

According to the DWC3 databook, this bit should only be set
after core and device/host mode initialization is performed.
Otherwise it could lead to enumeration failures.

Change-Id: I99096e2c502706baa6beec7da668fbd8cbd1daed
Signed-off-by: Jack Pham <jackp@codeaurora.org>