async-spdif-input

fix warnings

Granular documentation fix

some fixes (again) inputs i2s... sorry..

add DMAMEM, fix warnings

fix slave i2s output on teensy 4

Fix CHIP_I2S_CTRL on Init (SCLK=32*fs -> 64*fs)

I2S2: Cache handling

Implement Teensy-LC DAC audio playback

Pwm t4

Spdif-input

Input i2s: cache

PROGMEM -> FLASHMEM

Attention, only tested with my oscilloscopy, no audible test.

I'm a bit unsure about the different value(+120) for the MSB on Teensy. This may need a fix.
Also, T3 uses the 2.5xsamplerate - this is not implemented, too.

update

- switch to single-DMA architecture (was having to manually reset address/byte counter each time anyway, so no real benefit of using two)
- add 2-block output pipeline (mirroring Teensy 3.x)
- (sneak in timer frequency increase - may want to revert this)
- actiate DMA on timer expiration (required to use DMA from timer)
- have to manually enable DMA after setup and after each call to isr
- implement isr
	- check if dma is done (not sure this is required, but thought I saw it call once when it wasn't, and in theory you get called on errors too)
	- reset source buffer to point to other staging memory
	- re-enable dma at completion
	- otherwise similar to teensy3.x version

https://forum.pjrc.com/threads/58477-extend-Queue-object-for-Teensy-4-0-to-more-blocks