Fixes#979
Make sure to read the last byte of I2C data in the case where the IRQ happens
and the STOP signal is also asserted.
Also ensure all branches of the IRQ handler look at the same point in time
value for the IRQ status.
Add plumbing to allow `Wire`, `Serial1`, `SPI1` to map to the 2nd
hardware unit for devices where the PCB layout only brings out the
2nd port.
Fix the Seeedstudio XAIO pins
Fixes#594
The Pico HW seems to generate an interrupt on the end of every I2C
write cycle, even if the slave address wasn't actually targeted.
This would cause the onReceive method to be called with a 0-len
parameter for every write on the I2C bus.
Now, only call onReceive if there is 1 or more bytes of data available.
