drivers: i2c: tca954x: add support for idle disconnect

Add support for an optional "idle disconnect" feature in the TCA954x
I2C multiplexer. When enabled via the `i2c-mux-idle-disconnect` device
tree property, the driver will disconnect all channels after each
transfer. This helps avoid address conflicts when multiple multiplexers
are present on the same I2C bus.

Even if the I2C transfer fails, the driver will still attempt to
disconnect the channels to ensure the bus is left in a consistent state.
If the disconnect operation itself fails, its error code will be returned
unless the transfer already failed with a different error.

This implementation is inspired by the Linux kernel driver for PCA954x
I2C multiplexers. Special thanks to Ofir Shemesh for valuable suggestion.

Signed-off-by: Hank Wang <wanghanchi2000@gmail.com>