staging: dwc2: add microframe scheduler from downstream Pi kernel

The transfer scheduler in the dwc2 driver is pretty basic, not to
mention buggy. It works fairly well with just a couple of devices
plugged in, but if you add, say, multiple devices with periodic
endpoints, the scheduler breaks down and can't even enumerate all
the devices.

To improve this, import the "microframe scheduler" patch from the
driver in the downstream Raspberry Pi kernel, which is based on
the Synopsys vendor driver. The original patch came from Denx
(http://git.denx.de/?p=linux-denx.git

) and was commited to the
raspberrypi.org git tree by "popcornmix" (Dom Cobley).

I have added a driver parameter for this, enabled by default, in
case anyone has problems with it and needs to disable it. I don't
think we should add a DT binding for that, though, since I plan
to remove the option once any bugs are fixed.

[raspberrypi.org patch from Dom Cobley]
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
[adapted to dwc2 driver by Paul Zimmerman]
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>