extmod,docs: Add generic machine.CAN helpers & docs.

API is different to the original machine.CAN proposal, as numerous
shortcomings were found during initial implementation.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

docs/library/machine.CAN.rst

@@ -259,6 +259,7 @@ Classes
    machine.I2C.rst
    machine.I2CTarget.rst
    machine.I2S.rst
+   machine.CAN.rst
    machine.RTC.rst
    machine.Timer.rst
    machine.Counter.rst

docs/library/machine.rst

@@ -10,6 +10,7 @@ set(MICROPY_SOURCE_EXTMOD
     ${MICROPY_EXTMOD_DIR}/machine_adc.c
     ${MICROPY_EXTMOD_DIR}/machine_adc_block.c
     ${MICROPY_EXTMOD_DIR}/machine_bitstream.c
+    ${MICROPY_EXTMOD_DIR}/machine_can.c
     ${MICROPY_EXTMOD_DIR}/machine_i2c.c
     ${MICROPY_EXTMOD_DIR}/machine_i2c_target.c
     ${MICROPY_EXTMOD_DIR}/machine_i2s.c

extmod/extmod.cmake

@@ -5,6 +5,7 @@ SRC_EXTMOD_C += \
 	extmod/machine_adc.c \
 	extmod/machine_adc_block.c \
 	extmod/machine_bitstream.c \
+	extmod/machine_can.c \
 	extmod/machine_i2c.c \
 	extmod/machine_i2c_target.c \
 	extmod/machine_i2s.c \