usb: gadget: uvc: set req_size and n_requests based on the frame interval

usb: gadget: uvc: set req_size and n_requests based on the frame interval

This patch is removing the initial imprecise and limited calculation of
requests needed to be used from the queue_setup callback. It instead
introduces the uvc_video_prep_requests function which is called
immediately before the request allocation.

With the information of the usb frame interval length it is possible to
calculate the number of requests needed during one frame duration.

Based on the calculated number of requests and the imagesize we
calculate the actual size per request. This calculation has the benefit
that the frame data is equally distributed over all allocated requests.

When the req_size is not in the range for the actually configured
max_req_size configured for the overall bandwidth we fallback
to use the max_req_size instead.

Since this calculations are only important for isoc transfers we just
use max_request_size for bulk and skip it.

As video->req_size will be recalculated on every video_enable resetting
it to 0 is not necessary anymore.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20240403-uvc_request_length_by_interval-v7-5-e224bb1035f0@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>