usb: dwc2: Add dwc2_handle_gpwrdn_intr() handler

The GPWRDN interrupts are those that occur in both Host and
Device mode while core is in hibernated state.

Export dwc2_core_init to be able to use it in GPWRDN_IDSTS
interrupt handler.

Here we have duplicated init functions in host and gadget sides
so I have left things as it was(used corresponing functions for
host and gadget), maybe in the future we'll resolve this problem
and will use dwc2_core_init for both sides.

Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Artur Petrosyan <arturp@synopsys.com>
Signed-off-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>