ports/rp2/machine_i2s.c: Detect and deinitialize I2S instances on boot.

[marecl]

In reference to #14339

machine_i2s_init0 makes all of these pointers NULL without checking if there was a pointer already. Furthermore, garbage collector doesn't care enough to call I2S.deinit().
This created an issue, where invoking machine.soft_reset() would hard crash an entire board.
Fix is a check if machine_i2s_obj contains an object (assumed to be a valid machine_i2s_obj_t). If memory address is not NULL - object gets deinitialized. No further crashes are observed.

[dpgeorge]

Furthermore, garbage collector doesn't care enough to call I2S.deinit().

To fix that, finalisers should be enabled on the I2S object on all ports, following how esp32 does it. That requires two things:

1. Remove the #if MICROPY_PY_MACHINE_I2S_FINALISER guard from extmod/machine_i2s.c.
2. Make rp2, stm32, mimxrt ports all use mp_obj_malloc_with_finaliser() instead of mp_obj_malloc() in their mp_machine_i2s_make_new_instance() implementations.

[github-actions]

Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
     mimxrt:    +0 +0.000% TEENSY40
        rp2:   +32 +0.010% RPI_PICO
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS

[robert-hh]

If you do not want to follow the recommendation of Damien, this deinit should better be placed at the end of main() between the label soft_reset_exit: and the call to gc_sweep_all();. At that point the I2S data structure is still intact and mp_machine_i2s_deinit() can be called safely. After gc_sweep_all() has run, all allocated data elements can not be considered any more as valid, which includes the I2S object and it's buffers. So they must not be used in machine_i2s_init0(). You might have to create a function like machine_i2c_deinit_all() in machine_i2s.c which is called at behind label soft_reset_exit: in main.c.

[marecl]

If you do not want to follow the recommendation of Damien, this deinit should better be placed at the end of main() between the label soft_reset_exit: and the call to gc_sweep_all();. At that point the I2S data structure is still intact and mp_machine_i2s_deinit() can be called safely. After gc_sweep_all() has run, all allocated data elements can not be considered any more as valid, which includes the I2S object and it's buffers. So they must not be used in machine_i2s_init0(). You might have to create a function like machine_i2c_deinit_all() in machine_i2s.c which is called at behind label soft_reset_exit: in main.c.

I'll work on this, just don't have a lot of free time. I'd rather go with Damien's solution as it seems more appropriate and portable. I don't have other devboards, so most likely fixing it globally (like calling __del__ or __exit__) would free us from meddling with hardware.
Also, sorry about chaotic messaging in this thread but the only time I really have at hand is late at night :P