Add a new `esp32.PCNT` class that provides complete, low-level support to
the ESP32 PCNT pulse counting hardware units.
This can be used as a building block to implement the higher-level
`machine.Counter` and `machine.Encoder` classes.
This is enabled by default on all OG, S2, S3, C6 boards, but not on C3 (as
the PCNT peripheral is not supported).
Original implementation by: Jonathan Hogg <me@jonathanhogg.com>
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
Signed-off-by: Angus Gratton <angus@redyak.com.au>
