ARM: dts: aspeed-g6: Add aliases for mdio nodes

ARM: dts: aspeed-g6: Add aliases for mdio nodes

Add aliases for mdio nodes so that we can use name to lookup the
bus address of Aspeed SOC.

For example:
root@bletchley:~# cat /sys/firmware/devicetree/base/aliases/mdio0
/ahb/mdio@1e650000
root@bletchley:~# cat /sys/firmware/devicetree/base/aliases/mdio1
/ahb/mdio@1e650008
root@bletchley:~# cat /sys/firmware/devicetree/base/aliases/mdio2
/ahb/mdio@1e650010
root@bletchley:~# cat /sys/firmware/devicetree/base/aliases/mdio3
/ahb/mdio@1e650018

Signed-off-by: Potin Lai <potin.lai.pt@gmail.com>
Link: https://lore.kernel.org/r/20221025055046.1704920-1-potin.lai.pt@gmail.com
Signed-off-by: Joel Stanley <joel@jms.id.au>