Enumeration issues with external PHY

[Disasm]

Device fails to re-enumerate after firmware is updated. Power cycle is needed to trigger enumeration. This issue was observed on a board where external HS PHY is used. With internal HS PHY or FS PHY everything works ok.

Board: XCore407I

Steps to reproduce:

• Connect the board to a debugger
• Connect the USB_HS port to PC
• Build firmware (https://github.com/Disasm/usb-otg-workspace) and flash the device

cd example-xcore407i-board
cargo embed --release --example=serial --features hs

• Observe via dmesg that device doesn't enumerate

Introduced in: #28