dt-bindings: aspeed: Remove mention of deprecated compatibles

Guide readers away from using the aspeed,g[45].* compatible patterns.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20190724081313.12934-4-andrew@aj.id.au


Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>