usb: dwc3: Add maximum hw supported speed flag

Maximum hardware supported speed flag limits the maximum speed
of the usb controller to high or super. Adding this additional
flag as maximum_speed flag can be changed from different sources
such as power delivery stack.

Change-Id: I18f414e822b5525fe848a48384fac102cdae7b03
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>