dt-binding: eeprom: at24: add vcc-supply property

In some platforms, they disable the power-supply of eeprom due
to power consumption reduction. This patch add vcc-supply property.

Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>