usb: dwc3: Fall back to high speed when SSPHY fails

In some cases, it has been observed that SSPHY fails to initialized.
This change detects this condition and configures controller to work
into high speed mode only.

Change-Id: I50c4041d8572d0cdc4535812eebd10fc18b78e98
Signed-off-by: Mayank Rana <mrana@codeaurora.org>