GitLab

This change has no impact on vanilla MicroPython builds, but is intended to
avoid RP2's PIO implementation from trampling PIO usage in USER_C_MODULES.

This is consistent with PIOs tracking of used state machines and managed
programs, and makes working with PIO in USER_C_MODULES much less of an
uphill battle.

Since PIO deinit runs before gc_sweep_all it's impossible to work around
this wrinkle otherwise.  A module finalizer does not get the opportunity to
put the PIOs back into a state which wont crash rp2_pio_deinit.

Changes are:
- init: Avoid exclusive handlers being added to all PIOs and add them only
  when needed.
- deinit: Only remove handlers we have set.
- rp2_pio_irq: Add the exlusive handler if needed.
- rp2_state_machine_irq: Add the exclusive handler if needed.
Signed-off-by: Phil Howard <phil@gadgetoid.com>