usb: dwc3: make usb2 phy utmi interface configurable

Support to configure the UTMI+ PHY with an 8- or 16-bit
interface via DT. The UTMI+ PHY interface is a hardware
capability, and it's platform dependent. Normally, the
PHYIF can be configured during coreconsultant.

But for some specific USB cores(e.g. rk3399 SoC DWC3),
the default PHYIF configuration value is false, so we
need to reconfigure it by software.

Signed-off-by: William Wu <william.wu@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>