WIP: load dt properties

TODO: Document added bindings
WIP: Enable dwc2 for raspberry pi
staging: dwc2: Do not dump HCDMA register when dma is disabled

On the raspberry pi, this has been observed to cause a lockup when
reading this register with dma disabled.
staging: dwc2: Use irq_return_t for interrupt handlers

The top-level hcd interrupt handlers already used irq_return_t, but the
functions to which it delegates the actual work and the common irq
handler returned plain ints. In addition, they used the IRQ_RETVAL in
the wrong way (but because of the values of the various constants, this
didn't result in wrong behaviour).

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
[matthijs@stdin.nl: Split patch from bigger patch and added commit message]
Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
staging: dwc2: Add const to handling of dwc2_core_params

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
[matthijs@stdin.nl: Split patch from bigger patch and added commit message]
Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>