ARM: dts: aspeed: witherspoon: Enable checkstop and cooling gpio keys

Enable gpio-keys events for the checkstop and water/air cooled
gpios for use by applications on the Witherspoon system.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>