usb: dwc3: Enable l1_suspend_n signal for host mode

L1 suspend enables the PHY's utmi clock to be powered
off during L1 suspend which can save power during
audio playback using usb audio headphones

Change-Id: I9711ed625df119c48f4edddb8d1a0e48315e037b
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>