usb: dwc3: core: fix wrong OTG event regitser offset

This patch fixes the wrong OTG_EVT,OTG_EVTEN and OTG_STS register
offsets.

While at that, also add a missing register to debugfs regdump
utility.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>