dwc_otg: Enable NAK holdoff for control split transactions

Certain low-speed devices take a very long time to complete a
data or status stage of a control transaction, producing NAK
responses until they complete internal processing - the USB2.0
spec limit is up to 500mS. This causes the same type of interrupt
storm as seen with USB-serial dongles prior to c8edb238.

In certain circumstances, usually while booting, this interrupt
storm could cause SD card timeouts.
Merge pull request #380 from P33M/rpi-3.6.y

dwc_otg: Enable NAK holdoff for control split transactions