dwc-otg: FIQ: Fix "bad mode in data abort handler"

Create a semi-static mapping for the USB registers early in the boot
process, before additional kernel threads are started, so all threads
will have the mappings from the start. This avoids the need for
data aborts to lazily update them.

See: https://github.com/raspberrypi/linux/issues/2450



Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>