usb: dwc2: Move dwc2_readl/writel functions after hsotg structure

Moved dwc2_readl/writel functions after hsotg declaration for
adding hsotg structure to dwc2_readl/writel function prototypes.

Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Gevorg Sahakyan <sahakyan@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>