Get dwc2 working on octeon.

Get dwc2 working on octeon.
- transplant the clock setup code from octhci
- add a bus space tag to deal with dwc2 using little endian addressing
- bump up the rx fifo size, necessary for umass/sd to work

tested on an edgerouter lite, which can almost boot by itself now
ok uebayasi@ (various parts), miod@ (bus space bits)