usb: dwc2: Move gadget probe function into platform code

This patch will aggregate the probing of gadget/hcd driver into platform.c.
The gadget probe funtion is converted into gadget_init that is now only
responsible for gadget only initialization. All the gadget resources are now
handled by platform.c

Since the host workqueue will not get initialized if the driver is configured
for peripheral mode only. Thus we need to check for wq_otg before calling
queue_work().

Also, we move spin_lock_init to common location for both host and gadget that
is either in platform.c or pci.c.

We also move suspend/resume code to common platform code.

Lastly, move the "samsung,s3c6400-hsotg" binding into dwc2_of_match_table.

Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>