dt-bindings: mfd: Add compatible for the MediaTek MT6359 PMIC

This adds compatible for the MediaTek MT6359 PMIC.

Signed-off-by: Hsin-Hsiung Wang <hsin-hsiung.wang@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>