usb: gadget: dummy_hcd: add setup / cleanup of multiple HW intances

This patch creates & adds multiple instances of the HCD and UDC. We have
a new module option "num" which says how many emulated UDCs + HCDs we
want. The default value is one and currently the maximum is one as well.
This will change soon.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>