ARM: dts: aspeed: Add reg hints to syscon children

Fixes the following warnings:

    arch/arm/boot/dts/aspeed-g5.dtsi:209.28-226.6: Warning (avoid_unnecessary_addr_size): /ahb/apb/syscon@1e6e2000: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property
    arch/arm/boot/dts/aspeed-g4.dtsi:156.28-172.6: Warning (avoid_unnecessary_addr_size): /ahb/apb/syscon@1e6e2000: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>