Support USB External PHY and USB-SERIAL-JTAG coexistence

[ProfFan]

This can be achieved per the TRM (page 942).

The first part would eliminate the need to enable the internal PHY alongside with Wi-Fi which apparently is not recommended per the manual.

The second part would allow the USB and USB-JTAG to be used concurrently, which allows easy, debuggable development of USB peripherals.

[MabezDev]

This would be nice, something I wish I did for my keyboard. I don't think it should be that hard, but I don't know how to test it. Do you know of any devkits that use an external USB phy?

[ProfFan]

@MabezDev I don't know, but this seems to indicate a viable solution. I'll see if I can make something that has it and potentially ship to you guys?