Add ISO endpoint support

[elagil]

Adds support for ISO endpoints for both the STM32 OTG USB driver and the "regular" (newer?) USB driver.

[elagil]

For anyone who is reviewing this, find the USB packet buffer layouts that I used. They are relevant for the functions that read/write from/to the btable. The values in the btable are the addresses of the software packet buffers, and the received/transmitted buffer sizes.

For double-buffered endpoints, both RX and TX count and address fields are used for THE SAME direction (either RX or TX, never both). I hope that is clear from the comments in the code as well.

From RM0481 (STM32H5), where #[cfg(any(usbram_32_2048, usbram_32_1024))]

From RM0091 (STM32F0x1), where #[cfg(not(any(usbram_32_2048, usbram_32_1024)))]

[M3gaFr3ak]

This is a very important PR to make embassy usable for any audio-related USB stuff. I'm currently implementing USB Audio 2.0 and thanks to this PR, I have a successfully enumerating and streaming device!
When I'm finished, I'll try to PR an example.

[elagil]

@M3gaFr3ak I agree, that is what I needed it for. Very curious to see your UAC 2.0 implementation! I made UAC 1.0 in #3212, but would rather use 2.0 for USB high speed.

[Dirbaio]

thank you! looking great

[M3gaFr3ak]

@elagil This is the test implementation I'm currently doing: https://github.com/M3gaFr3ak/rp-usb-uac2
It's only using full speed, but that's enough for demoing. I don't actually do proper handling, it currently enumerates and the endpoints receive data. I've also modified embassy-usb to allow reuse of endpoints #2994 (I will still have to implement reconfiguration of endpoints, currently it just reuses them and doesnt change their buffer size etc).
I'll continue working on this until i have a loopback device working (speaker to mic)

Update:
My testimplementation is already working (echo device) in the test_old_embassy branch. Currently working on the endpoint-reuse.