usb: dwc3: make usb2 phy interface configurable in DT

usb: dwc3: make usb2 phy interface configurable in DT

Add snps,phyif_utmi_16_bits devicetree property. USB2 phy
interface is hardware property, and it's platform dependent,
so we need to configure it in devicetree to set the core to
support a UTMI+ PHY with an 8- or 16-bit interface.

And according to dwc3 databook, the GUSB2PHYCFG.USBTRDTIM
must set to the required values for the usb2 phy interface.

Change-Id: If1c636edc6be3c9a79b4b0b89737a925d8dd3abe
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>