staging: dwc2: platform device bindings

This adds a dwc_platform.ko module that can be loaded by using
compatible = "snps,dwc2" in a device tree.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
MIPS: ralink: Use the dwc2 driver for the rt305x USB controller
MIPS: ralink: Setup dma_mask for the rt305x dwc2 usb controller
staging: dwc2: Always release host channel after dequeueing

Previously, when an active urb was dequeued, its host channel would not
always be released.  There is some special handling for this in
dwc2_hc_chhltd_intr_dma, but when it was the last urb/qtd in its qh, a
safeguard in dwc2_hc_n_intr would short-circuit and prevent the regular
interrupt handlers from running, without releasing the channel.

This is easily triggered when using a 3G modem using the option driver.
Opening and closing any ttyUSBx device will eat up a host channel that
is forever unusable from that point on.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
staging: dwc2: toggle periodic debugging output separately

This adds a config option USB_DWC2_DEBUG_PERIODIC that allows debugging
output be suppressed for periodic transfers. This helps when debugging
non-periodic transfers while there are also periodic transfers going on
(both to make the debug output less polluted and to prevent all CPU time
going to debug messages).

In addition, a debug message from dwc2_hcd_is_status_changed is removed
entirely, since it often floods the log regardless of periodic
transfers.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>