ARM: dts: aspeed: cmm: Fixup I2C tree

Create all the i2c switches in device tree and use aliases to assign
child channels with consistent bus numbers.

Besides, "i2c-mux-idle-disconnect" is set for all the i2c switches to
avoid potential conflicts when multiple devices (beind the switches)
use the same device address.

Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>