usb: dwc3: remove debug event prints for endpoint events

Endpoint events can be received at a high rate, in which case
the debug prints increase cpu usage.
The existing counter mechanism is much more lightweight and provides
similar info.

Change-Id: If4e61bcf4cc47639265028b34c452d8a6caf2b6d
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>