usb: dwc3: gadget: Rewrite endpoint allocation flow

usb: dwc3: gadget: Rewrite endpoint allocation flow

The driver dwc3 deviates from the programming guide in regard to
endpoint configuration. It does this command sequence:

DEPSTARTCFG -> DEPXFERCFG -> DEPCFG

Instead of the suggested flow:

DEPSTARTCFG -> DEPCFG -> DEPXFERCFG

The reasons for this deviation were as follow, quoted:

	1) The databook says to do %DWC3_DEPCMD_DEPSTARTCFG for every
	   %USB_REQ_SET_CONFIGURATION and %USB_REQ_SET_INTERFACE
	   (8.1.5). This is incorrect in the scenario of multiple
	   interfaces.

	2) The databook does not mention doing more
	   %DWC3_DEPCMD_DEPXFERCFG for new endpoint on alt setting
	   (8.1.6).

Regarding 1), DEPSTARTCFG resets the endpoints' resource and can be a
problem if used with SET_INTERFACE request of a multiple interface
configuration. But we can still satisfy the programming guide
requirement by assigning the endpoint resource as part of
usb_ep_enable(). We will only reset endpoint resources on controller
initialization and SET_CONFIGURATION request.

Regarding 2), the later versions of the programming guide were updated
to clarify this flow (see "Alternate Initialization on SetInterface
Request" of the programming guide). As long as the platform has enough
physical endpoints, we can assign resource to a new endpoint.

The order of the command sequence will not be a problem to most
platforms for the current implementation of the dwc3 driver. However,
this order is required in different scenarios (such as initialization
during controller's hibernation restore). Let's keep the flow consistent
and follow the programming guide.

Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/c143583a5afb087deb8c3aa5eb227ee23515f272.1706754219.git.Thinh.Nguyen@synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>