usb: dwc2: Disable power down feature on Samsung SoCs

Power down feature of DWC2 module integrated in Samsung SoCs doesn't work
properly or needs some additional handling in PHY or SoC glue layer, so
disable it for now. Without disabling power down, DWC2 causes random memory
trashes and fails enumeration if there is no USB link to host on driver
probe.

Fixes: 03ea6d6e ("usb: dwc2: Enable power down")
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>