usb: dwc3: debugfs: Dump out IRQ timing statistics

This change helps to dump out different IRQ timing statistics
using debugfs entry.

Change-Id: I466144d8141f4236b9fb834dded93225b56d0422
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>