dt-bindings: pinctrl: aspeed: Convert AST2500 bindings to json-schema

Convert ASPEED pinctrl bindings to DT schema format using json-schema.

Cc: Johnny Huang <johnny_huang@aspeedtech.com>
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20190628023838.15426-4-andrew@aj.id.au


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>