dt-bindings: mfd: Initial commit of silergy,sy7636a.yaml

Initial support for the Silergy SY7636A Power Management chip
and regulator.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>