ARM: dts: aspeed: Migrate away from aspeed, g[45].* compatibles

Use the SoC-specific compatible strings instead.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>