ARM: dts: aspeed: zaius: fixed I2C bus numbers for pcie slots

The change to include ibm-power9-cfam.dtsi resulted in a renumbering
of all of the I2C bus numbers behind the on-board muxes.  This breaks
some tools which have hardcoded the bus numbers.

Add device tree aliases for the I2C buses routed through the PCIe slots
so that they return to their former numbers before the cfam change.

Signed-off-by: Robert Lippert <rlippert@google.com>
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>