fixed bug in i2c initialization and rs485 shutdown which prevents port 4 sensors from working

The RS485 driver outputs must be disabled when not in use,
as they're multiplexed with Port 4 I2C pins.

In addition, I2C pins on all sensors should have Pull Up Resistors disabled.
Otherwise this affects Port 4 operation since it has a Schottky barrier diode
at the outputs instead of the normal configuration for the other sensor ports.